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Share Based Compensation (Details) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
Share Based Compensation (Details) $ in Thousands	Dec. 10, 2019 item	May 23, 2018 shares	May 31, 2018 shares	Mar. 31, 2020 USD ($) shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 shares
Share-based compensation
Share-based compensation expense \| $				$ 4,209	$ 2,893
Stock options \| Class A common shares
Share-based compensation
Shares outstanding (in shares)				8,990,872		8,491,734
Number of options granted				1,455,250
First RSU Award
Share-based compensation
Share-based compensation expense \| $				$ 0
2018 Incentive Award Plan \| Class A common shares
Share-based compensation
Total number of common shares authorized to issue			4,466,500
Percentage of automatic increase in shares available for issue				4.00%
Additional shares authorized						2,197,505
Number of common shares available for future grant				3,226,660
2018 Incentive Award Plan \| Class A common shares \| Maximum
Share-based compensation
Percentage of automatic increase in shares available for issue			4.00%
Maximum number of common shares may be issued			27,915,000
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs)
Share-based compensation
Number of grants of RSU awards that a participant may receive \| item	2
Number of awards that will be earned or vest if the milestone date does not occur by the specified date \| item	0
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Earnout Level 1
Share-based compensation
Potential performance earnout percentage	100.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Earnout Level 2
Share-based compensation
Potential performance earnout percentage	50.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Earnout Level 3
Share-based compensation
Potential performance earnout percentage	25.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Earnout Level 4
Share-based compensation
Potential performance earnout percentage	0.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Upside Earnout Level 1
Share-based compensation
Potential performance earnout percentage	50.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Upside Earnout Level 2
Share-based compensation
Potential performance earnout percentage	25.00%
Rilonacept Long-term Incentive Plan \| Restricted Share Units (RSUs) \| Upside Earnout Level 3
Share-based compensation
Potential performance earnout percentage	0.00%
2015 Equity Incentive Plan \| Class A common shares
Share-based compensation
Total number of common shares authorized to issue		4,691,213		3,477,438
Number of shares no longer available for future grant		92,170
2015 Equity Incentive Plan \| Stock options
Share-based compensation
Voting power threshold percentage used to determine the exercise price for options				10.00%
Vesting percentage of options having four year vesting term on the first anniversary of the grant date				25.00%
Vesting percentage of options having six year vesting term on the first anniversary of the grant date				16.00%
2015 Equity Incentive Plan \| Stock options \| Employees
Share-based compensation
Vesting period				6 years
2015 Equity Incentive Plan \| Stock options \| Employees and non employees
Share-based compensation
Vesting period				4 years
2015 Equity Incentive Plan \| Stock options \| Minimum
Share-based compensation
Vesting period				4 years
2015 Equity Incentive Plan \| Stock options \| Maximum
Share-based compensation
Option term of incentive awards				10 years
Option term of awards for the persons possessing more than 10% of voting power				5 years
Vesting period				6 years
2015 Equity Incentive Plan \| Stock options \| Class A common shares
Share-based compensation
Minimum percentage of exercise price of the fair market value of shares for the persons possessing 10% or less of voting power				100.00%
Minimum percentage of exercise price of the fair market value of shares for the persons possessing more than 10% of voting power				110.00%
2018 Employee Share Purchase Plan \| Class A common shares
Share-based compensation
Total number of common shares authorized to issue			670,000
Automatic increase in number of shares available for issue						0
Number of common shares available for future grant				598,334
2018 Employee Share Purchase Plan \| Class A common shares \| Maximum
Share-based compensation
Percentage of automatic increase in shares available for issue		1.00%
Maximum number of common shares may be issued		6,420,000

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 106,336	$ 46,928
Short-term investments	97,870	186,452
Prepaid expenses and other current assets	8,849	8,247
Total current assets	213,055	241,627
Property and equipment, net	5,804	6,398
Operating lease right-of-use assets	1,629	1,927
Restricted cash	210	210
Deferred tax assets	5,410	4,372
Total assets	226,108	254,534
Current liabilities:
Accounts payable	4,274	5,693
Accrued expenses	13,379	20,415
Operating lease liabilities	1,689	1,697
Other current liabilities		25
Total current liabilities	19,342	27,830
Non-current liabilities:
Non-current operating lease liabilities	551	955
Other long-term liabilities	381	326
Total liabilities	20,274	29,111
Commitments and contingencies (Note 12)
Shareholders’ equity:
Additional paid-in capital	588,090	581,467
Accumulated other comprehensive income	240	33
Accumulated deficit	(382,511)	(356,092)
Total shareholders’ equity	205,834	225,423
Total liabilities and shareholders’ equity	226,108	254,534
Class A common shares
Shareholders’ equity:
Common stock value	6	6
Class B common shares
Shareholders’ equity:
Common stock value	1	1
Class A1 common shares
Shareholders’ equity:
Common stock value	4	4
Class B1 common shares
Shareholders’ equity:
Common stock value	$ 4	$ 4

CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Thousands	Common Shares Follow-On Offering	Common Shares Private Placement	Common Shares	Additional Paid-In Capital Follow-On Offering	Additional Paid-In Capital Private Placement	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Follow-On Offering	Private Placement	Total
Balance at the beginning of the period at Dec. 31, 2018			$ 13			$ 473,483	$ (4)	$ (194,225)			$ 279,267
Balance at the beginning of the period (in shares) at Dec. 31, 2018			49,489,647
Changes in equity
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs	$ 2			$ 48,474	$ 34,511				$ 48,476	$ 34,511
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs (in shares)	2,816,110	2,000,000
Common shares issued or to be issued in connection with the acquisition of all issued and outstanding equity securities of Primatope Therapeutics, Inc.						7,000					7,000
Common shares issued or to be issued in connection with the acquisition of all issued and outstanding equity securities of Primatope Therapeutics, Inc. (in shares)			337,008
Exercise of options						181					181
Exercise of options (in shares)			50,070
Share-based compensation expense						2,893					2,893
Unrealized gain on short-term investments							12				12
Net loss								(65,821)			(65,821)
Balance at the end of the period at Mar. 31, 2019			$ 15			566,542	8	(260,046)			306,519
Balance at the end of the period (in shares) at Mar. 31, 2019			54,692,835
Balance at the beginning of the period at Dec. 31, 2019			$ 15			581,467	33	(356,092)			225,423
Balance at the beginning of the period (in shares) at Dec. 31, 2019			54,937,628
Changes in equity
Exercise of options						2,414					2,414
Exercise of options (in shares)			643,867
Share-based compensation expense						4,209					4,209
Unrealized gain on short-term investments							207				207
Net loss								(26,419)			(26,419)
Balance at the end of the period at Mar. 31, 2020			$ 15			$ 588,090	$ 240	$ (382,511)			$ 205,834
Balance at the end of the period (in shares) at Mar. 31, 2020			55,581,495

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Cash and Cash Equivalents

The Company classifies deposits in banks, money market funds and cash invested temporarily in various instruments with maturities of three months or less at the time of purchase as cash and cash equivalents. At March 31, 2020 and December 31, 2019, cash and cash equivalents consisted principally of U.S. Treasury notes, amounts held in money market accounts and cash on deposit at commercial banks.

Short-Term Investments

The Company generally invests its excess cash in money market funds and short-term investments in U.S. Treasury notes. Such investments included in short-term investments on the Company's consolidated balance sheets are considered available-for-sale debt securities and are reported at fair value with unrealized gains and losses included as a component of shareholders’ equity. Realized gains and losses, if any, on short-term investments are included in interest income.

The Company evaluates its short-term investments with unrealized losses for other-than-temporary impairment. When assessing short-term investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Reclassifications

The Company reclassified certain prior year balances on our consolidated statements of cash flows to conform to current year presentation. Those balances related to prepaid expenses and other assets and non-cash lease expense. These reclassifications had no effect on our net cash used by operating activities or our consolidated statements of operations and comprehensive loss.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents and short-term investments. At March 31, 2020 and December 31, 2019, substantially all of the Company’s cash, cash equivalents and short-term investments were held at two financial institutions. The Company generally maintains balances in various operating accounts at financial institutions that management believes to be of high credit quality, in amounts that may exceed federally insured limits. The Company has not experienced any losses related to its cash, cash equivalents and short-term investments and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Restricted Cash

In conjunction with the Company’s lease agreement entered into in March 2018 (see Note 5), the Company maintains a letter of credit for the benefit of the landlord. As of March 31, 2020 and December 31, 2019, the underlying cash balance of $210 securing this letter of credit, was classified as non‑current in its consolidated balance sheet.

Fair Value Measurements

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s restricted cash, which is held in a money market fund, is carried at fair value, determined based on Level 1 inputs in the fair value hierarchy described above (see Note 3). The Company’s cash equivalents and short-term investments, consisting of money market accounts and U.S. Treasury notes, are carried at fair value, determined based on Level 1 and 2 inputs in the fair value hierarchy described above (see Note 3). The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short‑term nature of these assets and liabilities.

Leases

In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which set forth the principles for recognition, measurement, presentation and disclosure of lease arrangements to enhance the transparency and comparability of financial reporting related to the arrangements. ASU 2016-02, including subsequently issued amendments, is collectively referred to as Accounting Standards Codification, Leases (Topic 842) (“ASC 842”). The Company adopted the standard on January 1, 2019 using the modified retrospective transition approach as applied to leases existing as of the adoption date. The standard is applied to all leases entered into after the initial adoption date.

At the inception of an arrangement, the Company determines whether the arrangement is or contains a “lease” as defined by ASC 842. A lease is an arrangement, or part of an arrangement, that conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. The Company determines if the arrangement conveys the right to control the use of an identified asset for a period of time. It assesses throughout the period of use whether the Company has both of the following (1) the right to obtain substantially all of the economic benefits from use of the identified asset and (2) the right to direct the use of the identified asset. This determination is reassessed if the terms of the arrangement are changed. Leases are classified as operating or finance leases based on the terms of the lease agreement and certain characteristics of the identified asset. Right-of-use (“ROU”) assets and lease liabilities are recognized at lease commencement date based on the present value of the minimum future lease payments.

Most leases with a term greater than one year are recognized on the balance sheet as ROU assets with corresponding lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize leases with a term of one year or less on its balance sheet. Operating leases, ROU assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the ROU assets may be required for items such as incentives received. The interest rate implicit in lease arrangements is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment.

In accordance with the guidance in ASU 2016-02, components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.); then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components.

Although separation of lease and non-lease components is required, certain practical expedients are available. Companies may elect the practical expedient to not separate lease and non-lease components. In which case, the Company would account for each lease component and the related non-lease component together as a single component. The Company has elected to account for the lease and non-lease components of each of its operating leases as a single lease component and allocate all of the arrangement consideration to the lease component only. The lease component results in an operating ROU asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop product candidates, including personnel expenses, share‑based compensation expense, allocated facility‑related and depreciation expenses, third‑party license fees and external costs of outside vendors engaged to conduct preclinical and clinical development activities and clinical trials as well as to manufacture clinical trial materials. Non‑refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. Milestone and other payments made to third parties with respect to in-process research and development, in accordance with the Company’s license, acquisition and other similar agreements are expensed when determined to be probable and estimable.

Research Contract Costs and Accruals

The Company has entered into various research and development-related contracts with companies both inside and outside of the United States. The related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company's estimates. The Company's historical accrual estimates have not been materially different from the actual costs.

Share‑Based Compensation

The Company measures all share-based awards granted to employees and directors based on their fair value on the date of grant. The Company issues share-based awards with both service-based vesting conditions and performance-based vesting conditions. The Company recognizes compensation expense for awards with service conditions on a straight-line basis over the requisite service period. For awards with performance conditions, the Company recognizes compensation expense when the achievement of the performance milestone is probable and estimable through the vest date.

For share-based awards granted to consultants and non-employees, compensation expense is recognized over the vesting period of the awards, which is generally the period during which services are rendered by such consultants and non-employees until completed.

The Company classifies share-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified.

The fair value of each option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected share price volatility, the expected term of the award, the risk-free interest rate, and expected dividends (see Note 8). Prior to May 2018, the Company was a private company and, accordingly, lacks company-specific historical and implied volatility information for its shares. Therefore, it estimates its expected share price volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. The expected term of the Company’s options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common shares and does not expect to pay any cash dividends in the foreseeable future.

The fair value of each restricted share unit award is based on the closing price of the Company’s Class A common shares on the date of grant. Restricted share unit awards with an associated performance condition are evaluated on a regular basis for probability of achievement, to determine the timing of recording share-based compensation expense in the Company’s consolidated statements of operations and comprehensive loss.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders. For the three months ended March 31, 2020 and 2019, the Company’s other comprehensive loss was comprised of unrealized gain (loss) on short-term investments as well as cumulative translation adjustments, net of tax.

Net Loss per Share

The Company follows the two‑class method when computing net loss per share as the Company has issued shares that meet the definition of participating securities. The two‑class method determines net loss per share for each class of common shares and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two‑class method requires income available to common shareholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Basic net loss per share attributable to common shareholders is computed by dividing the net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period. Diluted net loss attributable to common shareholders is computed by adjusting net loss attributable to common shareholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common shareholders is computed by dividing the diluted net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options and unvested restricted common shares are considered potential dilutive common shares.

In periods in which the Company reports a net loss attributable to common shareholders, diluted net loss per share attributable to common shareholders is the same as basic net loss per share attributable to common shareholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common shareholders for the three months ended March 31, 2020 and 2019.

Income Taxes

As an exempted company incorporated under the laws of Bermuda, the Company is principally subject to taxation in Bermuda. Under the current laws of Bermuda, tax on a company’s income is assessed at a zero percent tax rate. As a result, the Company has not recorded any income tax benefits from losses incurred in Bermuda during each reporting period, and no net operating loss carryforwards will be available to the Company for those losses. The Company’s wholly owned U.S. subsidiaries, Kiniksa US and Primatope, are subject to federal and state income taxes in the United States. The Company’s wholly owned subsidiary Kiniksa UK, and its wholly owned subsidiaries, Kiniksa Germany and Kiniksa France, are subject to taxation in their respective countries. Certain of the Company’s subsidiaries, primarily Kiniksa US, operate under cost-plus arrangements.

The Company’s benefit for income taxes primarily relates to credits generated by its wholly owned subsidiary, Kiniksa US. The benefit for income taxes is a result of the taxable income earned by Kiniksa US under its cost-plus arrangement offset in part by tax benefits from the U.S. federal and state research and development tax credits, the Foreign Derived Intangible Income (“FDII”) deduction and share-based compensation taxable events. FDII was enacted as part of the tax reform enacted by the United States in December 2017, generally referred to as the U.S. Tax Cuts and Jobs Act with additional proposed regulations and guidance issued in 2019. Upon the completion of the Company’s assessment, the Company has included the tax impact of FDII in its income tax expense for the three months ended March 31, 2020, based on its understanding of the rules available at the time of this filing. However, the amounts recorded could be impacted in the future when the proposed regulations and guidance are finalized.

The Company provides for income taxes on an interim basis according to management’s estimate of the effective tax rate expected to be applicable for the full fiscal year. Subsidiaries with losses for which no benefit can be claimed are excluded from this calculation, and their tax is recorded discretely in the period it arises. Certain other items such as changes in tax rates, tax benefits or expense related to settlements of share-based payment awards, and uncertain tax positions are treated as discrete items and are recorded in the period in which they arise.

Recently Adopted Accounting Pronouncements

In June 2016, the FASB, issued ASU 2016-13, Financial Instruments: Credit Losses (Topic 326), as clarified in ASU 2019-04 and ASU 2019-05. The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than-temporary impairments on investment securities are recorded. The standard became effective for the Company beginning on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other— Internal-Use Software (Subtopic 350-40) (“ASU 2018-15”), which amends ASC 350-40 to address a customer’s accounting for implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 aligns the accounting for costs incurred to implement a CCA that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. Specifically, the ASU amends ASC 350 to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply ASC 350-40 to determine which implementation costs should be capitalized in a CCA that is considered a service contract. The standard became effective for the Company beginning on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

Recently Issued Accounting Pronouncements

In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740)(“ASU 2019-12”). The objective of the standard is to improve areas of GAAP by removing certain exceptions permitted by ASC Topic 740 Income Taxes and clarifying existing guidance to facilitate consistent application. The standard will become effective for the Company beginning on January 1, 2021. The Company is currently evaluating the new standard to determine the potential impact of ASU 2019-12 on its consolidated financial statements and related disclosures.

License and Acquisition Agreements	3 Months Ended
License and Acquisition Agreements	Mar. 31, 2020
License and Acquisition Agreements
License and Acquisition Agreements	9. License and Acquisition Agreements Biogen Asset Purchase Agreement In September 2016, the Company entered into an asset purchase agreement (the "Biogen Agreement") with Biogen MA Inc. ("Biogen") to acquire all of Biogen's right, title and interest in and to certain assets used in or relating to vixarelimab (KPL-716) and other antibodies covered by certain patent rights, including patents and other intellectual property rights, clinical data, know-how, and clinical drug supply. In addition, Biogen granted to the Company a non-exclusive, sublicensable, worldwide license to certain background patent rights related to the vixarelimab program. The Company is obligated to use commercially reasonable efforts to develop and commercialize such acquired products. In exchange for these rights, the Company made an upfront payment to Biogen of $11,500 and a technology transfer payment of $500. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment and technology transfer payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. Under the Biogen Agreement, the Company is obligated to make milestone payments to Biogen of up to $179,000 upon the achievement of specified clinical and regulatory milestones in multiple indications in various territories, including milestone payments of $4,000 and $10,000 paid during the year ended December 31, 2017 and the year ended December 31, 2019, respectively, each payment was associated with the achievement of a specified clinical milestone event. No milestones were achieved or paid during the three months ended March 31, 2020. Additionally, the Company could be obligated to make up to an aggregate of up to $150,000 of payments upon the achievement of specified annual net sales milestones and to pay tiered royalties on escalating tiers of annual net sales of licensed products starting in the high single-digit percentages and ending below the teens. The Company also agreed to pay certain obligations under third‑party contracts retained by Biogen that relate to the vixarelimab program. Under these retained contracts, the Company paid a one‑time upfront sublicense fee of $150 and is obligated to pay insignificant annual maintenance fees as well as clinical and regulatory milestone payments of up to an aggregate of $1,575. The Biogen Agreement will terminate upon the expiration of all payment obligations with respect to the last product in all countries in the territory. The Company has the right to terminate the agreement with 90 days’ prior written notice. Both parties may terminate by mutual written consent or in the event of material breach of the agreement by the other party that remains uncured for 90 days (or 30 days for payment‑related breaches). During the three months ended March 31, 2020, the Company recorded research and development expense of $64, primarily related to a milestone and the annual maintenance fee both in connection with the retained contracts. During the three months ended March 31, 2019, the Company recorded research and development expense of $10,002 primarily related to an accrued milestone associated with the achievement of a specified clinical milestone event due under the Biogen Agreement. Novo Nordisk License Agreement In August 2017, the Company entered into a license agreement (the “Novo Nordisk Agreement”) with Novo Nordisk A/S (“Novo Nordisk”), pursuant to which the Company was granted an exclusive, sublicensable, worldwide license under certain intellectual property rights controlled by Novo Nordisk to make, use, develop and commercialize KPL‑045 for all indications. In consideration for the license, the Company made an upfront payment of $1,500 to Novo Nordisk. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. In January 2020, the Company terminated the Novo Nordisk Agreement in accordance with the terms and conditions of the agreement. The Company did not record any research and development expense during the three months ended March 31, 2020 and 2019, in connection with milestone payments due under the Novo Nordisk Agreement. Primatope Stock Purchase Option Agreement In September 2017, the Company entered into a stock purchase option agreement (the “Primatope Agreement”) with Primatope Therapeutics, Inc. (“Primatope”), pursuant to which the Company was granted a license to certain intellectual property rights owned or controlled by Primatope to research, develop, and manufacture the preclinical antibody, KPL‑404. The agreement provided the Company with an exclusive call option to purchase 100% of the equity securities of Primatope. Upon execution of the agreement, the Company made $500 in upfront payments for the initial option period through April 2018 (the “Initial Option Period”). The Primatope Agreement allowed for up to three extensions of the Initial Option Period through January 2019 (including the initial option period, the “Option Period”) for total extension payments of up to $800. Through December 31, 2018, the Company made payments totaling $800 to extend the Option Period to January 15, 2019. During the Option Period, the Company could conduct research and preclinical work to assess the viability of the asset. The Company determined that the call option represented a variable interest in Primatope and that Primatope is a VIE. However, as the Company had no ability to control the board of directors or direct the ongoing activities of Primatope during the Option Period, the Company did not have power over the activities that most significantly impact Primatope’s economic performance and was not the primary beneficiary of Primatope. As a result, the Company did not consolidate the assets, liabilities, and results of operations of Primatope. In January 2019, the Company exercised the call option and in March 2019, the Company acquired all of the issued and outstanding equity securities of Primatope (the “Primatope Acquisition”) in exchange for $18,000 comprised of upfront consideration of $10,000 at closing and milestone payments of $5,000, which had been achieved as of the closing date, and in June 2019, the Company made the final milestone payment of $3,000, which was achieved during the year ended December 31, 2019 following the closing, each paid in a combination of cash and Class A common shares (inclusive of escrow and holdback amounts) in accordance with the Primatope Agreement. At the closing of the Primatope Acquisition, Primatope became a wholly owned subsidiary of the Company and the acquisition was accounted for as an asset acquisition as it did not meet the definition of a business. The Company recorded the upfront payment and milestone payments as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. During the three months ended March 31, 2020, the Company did not incur any research and development expense directly in connection with milestone or other payments related to the Primatope Acquisition or the Primatope Agreement. During the three months ended March 31, 2019, the Company recorded research and development expense of $18,000 related to the Primatope Acquisition. Beth Israel Deaconess Medical Center License Agreement As a result of the Primatope Acquisition, the Company acquired the rights to an exclusive license to certain intellectual property rights controlled by Beth Israel Deaconess Medical Center, Inc. (“BIDMC”) to make, use, develop and commercialize KPL-404 (the “BIDMC Agreement”). Under the BIDMC Agreement, the Company is solely responsible for all development, regulatory and commercial activities and costs. The Company is also responsible for costs related to filing, prosecuting and maintaining the licensed patent rights. Under the BIDMC Agreement, the Company is obligated to pay an insignificant annual maintenance fee as well as clinical and regulatory milestone payments of up to an aggregate of $1,200 to BIDMC. The Company is also obligated to pay a low single-digit royalty on annual net sales of products licensed under the agreement. The Company did not incur any research and development expense in connection with the BIDMC Agreement during the three months ended March 31, 2020 and 2019. Regeneron License Agreement In September 2017, the Company entered into a license agreement (the “Regeneron Agreement”) with Regeneron Pharmaceuticals, Inc. (“Regeneron”), pursuant to which the Company has been granted an exclusive, sublicensable license under certain intellectual property rights controlled by Regeneron to develop and commercialize rilonacept in certain fields and territories. The Company is obligated to use commercially reasonable efforts to develop and commercialize such licensed products. In exchange for these rights, the Company made an upfront payment of $5,000. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. Under the Regeneron Agreement, the Company is also obligated to make payments to Regeneron of up to an aggregate of $27,500 upon the achievement of specified regulatory milestones. Upon commercialization of the licensed products, the parties will share profits equally for all commercial products, after deducting certain commercialization expenses subject to specified limits. Under the Regeneron Agreement, the Company is solely responsible for all development and commercialization activities and costs in its territories. The Company is also responsible for costs related to the filing, prosecution and maintenance of certain licensed patent rights. The parties also entered into a clinical supply agreement under which Regeneron agreed to manufacture the developed product during the clinical phase. During the three months ended March 31, 2020, the Company did not incur any research and development expense related to the purchase of drug materials under this agreement. During the three months ended March 31, 2019, the Company recorded research and development expense of $515, related to the purchase of drug materials under this agreement. As of March 31, 2020 and December 31, 2019, the Company had non-cancelable purchase commitments under the clinical supply agreement (see Note 12). The Regeneron Agreement will expire when the Company is no longer developing or commercializing any licensed product under the Regeneron Agreement. Either party may terminate the agreement upon the other party’s insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured for 90 days (or 30 days for payment‑related breaches). Regeneron has the right to terminate the agreement if the Company suspends its development or commercialization activities for a consecutive 12‑month period or does not grant a sublicense to a third‑party to perform such activities, or if the Company challenges any of the licensed patent rights. The Company may terminate the agreement at any time that is 18 months after the effective date of the agreement with 180 days’ written notice or with one year’s written notice if the Company terminates the agreement following U.S. marketing approval of a rilonacept product developed by the Company. The Company may also terminate the agreement with three months’ written notice if the products are determined to have certain safety concerns. The Company did not incur any research and development expense directly related to milestone payments due under the Regeneron Agreement during the three months ended March 31, 2020 and 2019. MedImmune License Agreement In December 2017, the Company entered into a license agreement (the “MedImmune Agreement”) with MedImmune, Limited (“MedImmune”), pursuant to which MedImmune granted the Company an exclusive, sublicensable, worldwide license to certain intellectual property rights to make, use, develop and commercialize mavrilimumab. Under the MedImmune Agreement, the Company also acquired reference rights to relevant manufacturing and regulatory documents and MedImmune’s existing supply of mavrilimumab drug substance and product. The Company is obligated to use commercially reasonable efforts to develop and commercialize the licensed products. In exchange for these rights, the Company made an upfront payment of $8,000. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. In addition, the Company is obligated to make clinical, regulatory and initial sales milestone payments of up to $72,500 in aggregate for the first two indications, including, a $5,000 pass‑through payment due upon the achievement of a specified clinical milestone event which was met in the fourth quarter of 2018. Also included is a milestone payment of $10,000 due upon the earlier to occur of a specified regulatory milestone and December 31, 2018, unless the MedImmune Agreement is earlier terminated by either party. As of December 31, 2018 and 2017, the Company determined that the payment related to this milestone was probable and, therefore, recognized research and development expense and an accrued milestone of $10,000 during the year ended December 31, 2017. During the year ended December 31, 2019, the Company made both the $5,000 and $10,000 previously accrued milestone payments in accordance with the MedImmune Agreement. In addition, the Company is obligated to make clinical and regulatory milestone payments of up to $15,000 in the aggregate for each subsequent indication. The Company is obligated to make milestone payments to MedImmune of up to $85,000 upon the achievement of annual net sales thresholds up to, but excluding, $1,000,000 in annual net sales as well as additional milestone payments aggregating up to $1,100,000 upon the achievement of additional specified annual net sales thresholds starting at $1,000,000 and higher. The Company has also agreed to pay tiered royalties on escalating tiers of annual net sales of licensed products starting in the low double‑digit percentages and ending at twenty percent. Royalty rates are subject to reductions upon certain events. The Company is solely responsible for all development, manufacturing, and commercial activities and costs of the licensed products, including clinical studies or other tests necessary to support the use of a licensed product. The Company is also responsible for costs related to the filing, prosecution and maintenance of the licensed patent rights. The MedImmune Agreement will expire upon the expiration of the royalty term in the last country for the last indication, as defined in the agreement. Either party may terminate the agreement upon the other party’s insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured for 90 days. MedImmune has the right to terminate the agreement if the Company challenges any of the licensed patent rights. The Company may terminate the agreement at any time upon 90 days’ prior written notice. During the three months ended March 31, 2020 and 2019, the Company did not record research and development expense in connection with milestone payments due under the MedImmune Agreement. Kite Clinical Collaboration Agreement In December 2019, the Company entered into a clinical collaboration (the “Kite Agreement”) with Kite Pharma, Inc., a Gilead Company (“Kite”), to initiate a Phase 2 clinical trial evaluating the combination of Yescarta (axicabtagene ciloleucel) and mavrilimumab in relapsed or refractory large B-Cell lymphoma. The objective of the Phase 2 trial is to determine the effect of mavrilimumab on the safety of Yescarta. Treatment related induction of GM-CSF has been identified through clinical, translational and preclinical studies as a potential key signal associated with side effects of chimeric antigen receptor T, or CAR T, cell therapy. Preclinical evidence suggest the potential for interruption of GM-CSF signaling to disrupt CAR T cell mediated inflammation without disrupting anti-tumor activity. Kite will be the sponsor of this study and responsible for its conduct. Under the Kite Agreement, Kite and the Company agreed to share a portion of the costs incurred in conducting the study. The Kite Agreement will expire on the one-year anniversary of the date that Kite provides the clinical study report to the Company or unless otherwise terminated in accordance with the Kite Agreement. The Company evaluated the agreement and determined all costs and expenses will be recognized as incurred as research and development expenses. During the three months ended March 31, 2020, the Company did not record any research and development expense in connection with the Kite Agreement.

Share-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Share-Based Compensation

Schedule of share option activity under the Plans


		Weighted
	Number of	Average
	Shares	Fair Value
Outstanding as of December 31, 2019	8,491,734	$	7.68
Granted	1,455,250	$	10.74
Exercised	(643,867)	$	2.50
Forfeited	(234,919)	$	10.89
Cancelled	(77,326)	$	16.72
Outstanding as of March 31, 2020	8,990,872	$	8.39
Options exercisable as of March 31, 2020	3,176,450	$	8.26
Options unvested as of March 31, 2020	5,814,422	$	9.63

Schedule of stock option valuation assumptions presented on weighted-average basis


	Three Months Ended
	March 31,
	2020		2019
Risk-free interest rate	0.82	%	2.58	%
Expected term (in years)	6.25		6.25
Expected volatility	79.83	%	78.18	%
Expected dividend yield	0	%	0	%

Schedule of restricted share activity


		Weighted
		Average
	Number of	Grant Date
	Shares	Fair Value
Unvested RSUs as of December 31, 2019	328,296	$	12.93
Granted	—	$	—
Vested	—	$	—
Forfeited	(26,253)	$	12.93
Unvested RSUs as of March 31, 2020	302,043	$	12.93

Schedule of share-based compensation expense was classified in the consolidated statements of operations and comprehensive loss


	Three Months Ended
	March 31,
	2020		2019
Research and development expenses	$	1,769	$	1,187
General and administrative expenses		2,440		1,706
	$	4,209	$	2,893

Share-Based Compensation

3 Months Ended

Mar. 31, 2020

Share-Based Compensation

Share-Based Compensation

8. Share‑Based Compensation

2018 Incentive Award Plan

In May 2018, the Company’s board of directors and shareholders approved the 2018 Incentive Award Plan (the “2018 Plan”), which became effective on May 23, 2018. The 2018 Plan provides for the grant of incentive share options, nonqualified share options, share appreciation rights, restricted shares, dividend equivalents, restricted share units and other share- or cash- based awards. Upon the effectiveness of the 2018 Plan, the Company ceased granting awards under its 2015 Equity Incentive Plan (as amended, the “2015 Plan” together with the 2018 Plan, the “Plans”).

A total of 4,466,500 Class A common shares were initially reserved for issuance under the 2018 Plan. The number of Class A common shares that may be issued under the 2018 Plan will automatically increase on each January 1, beginning in 2019 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2028, equal to the lesser of (i) 4% of the Class A common shares outstanding (on an as‑converted basis) on the final day of the immediately preceding calendar year and (ii) a smaller number of Class A common shares determined by the Company’s board of directors. In December 2019, the board of directors approved the automatic increase as of January 1, 2020 of 2,197,505 shares, equal to 4% of the as-converted Class A common shares outstanding on December 31, 2019. No more than 27,915,000 Class A common shares may be issued under the 2018 Plan upon the exercise of incentive options. The Class A common shares underlying any awards issued under the 2018 Plan or the 2015 Plan that on or after the effective date of the 2018 Plan expire, lapse unexercised or are terminated, exchanged for cash, surrendered, repurchased, canceled without having been fully exercised or forfeited under the 2018 Plan or the 2015 Plan will be added back to the Class A common shares available for issuance under the 2018 Plan. As of March 31, 2020, 3,226,660 shares remained available for future grant.

2015 Equity Incentive Plan

Until May 23, 2018 (the effective date of the 2018 Plan), the 2015 Plan provided for the Company to grant incentive share options, nonqualified share options, share grants and other share‑based awards to employees and non‑employees to purchase the Company’s Class A common shares. On the effective date of the 2018 Plan, the Company ceased granting awards under the 2015 Plan. At that time, the 4,691,213 Class A common shares subject to outstanding awards under the 2015 Plan remained reserved for issuance under the plan pursuant such awards and the 92,170 Class A common shares that had been available for future grant under the 2015 Plan were no longer authorized and reserved for issuance or available for future grant under the 2015 Plan.

As of March 31, 2020, there were 3,477,438 Class A common shares subject to outstanding awards under the 2015 Plan and reserved for issuance under the 2015 Plan pursuant to such awards. On May 23, 2018, the effective date of the 2018 Plan, the Company ceased granting awards under the 2015 Plan and no Class A common shares were available for future grant under the 2015 Plan in connection with the 2018 Plan becoming effective. However, the 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. Class A common shares subject to awards granted under the 2015 Plan that are forfeited, lapse unexercised or are settled in cash become available for issuance under the 2018 Plan.

The exercise price for incentive share options was determined by the Company’s board of directors. All incentive share options granted to any person possessing 10% or less of the total combined voting power of all classes of shares could not have an exercise price of less than 100% of the fair market value of the Class A common shares on the grant date. All incentive share options granted to any person possessing more than 10% of the total combined voting power of all classes of shares could not have an exercise price of less than 110% of the fair market value of the Class A common shares on the grant date. The option term for incentive share options could not be greater than 10 years. Incentive share options granted to persons possessing more than 10% of the total combined voting power of all classes of shares could not have an option term of greater than five years. The vesting period for equity‑based awards was determined by the board of directors, which was generally four to six years. For awards granted to employees and non‑employees with four‑year vesting terms, 25% of the option vests on the first anniversary of the grant date and the remaining shares vest equally each month for three years thereafter. For awards granted to employees with six‑year vesting terms, 16% of the option vests on the first anniversary of the grant date and the remaining shares vest based on a predetermined vesting schedule for five years thereafter.

2018 Employee Share Purchase Plan

In May 2018, the Company’s board of directors and shareholders approved the 2018 Employee Share Purchase Plan (the “2018 ESPP”), which became effective on May 23, 2018. A total of 670,000 Class A common shares were initially reserved for issuance under the 2018 ESPP. The number of Class A common shares that may be issued under the 2018 ESPP will automatically increase on each January 1, beginning in 2019 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2028, equal to the lesser of (i) 1% of the Class A common shares outstanding (on an as‑converted basis) on the final day of the immediately preceding calendar year and (ii) a smaller number of Class A common shares determined by the Company’s board of directors, provided that no more than 6,420,000 Class A common shares may be issued under the 2018 ESPP. As of March 31, 2020, 598,334 Class A common shares were available for future issuance under the 2018 ESPP. In December 2019, the Company’s board of directors determined that the January 1, 2020 automatic increase in shares available under the 2018 ESPP would be zero shares.

Options

Share option activity under the Plans is summarized as follows:


		Weighted
	Number of	Average
	Shares	Fair Value
Outstanding as of December 31, 2019	8,491,734	$	7.68
Granted	1,455,250	$	10.74
Exercised	(643,867)	$	2.50
Forfeited	(234,919)	$	10.89
Cancelled	(77,326)	$	16.72
Outstanding as of March 31, 2020	8,990,872	$	8.39
Options exercisable as of March 31, 2020	3,176,450	$	8.26
Options unvested as of March 31, 2020	5,814,422	$	9.63

Option Valuation

The assumptions that the Company used to determine the grant‑date fair value of options granted to employees and directors under the Plans during the three months ended March 31, 2020 and 2019 were as follows, presented on a weighted‑average basis:


	Three Months Ended
	March 31,
	2020		2019
Risk-free interest rate	0.82	%	2.58	%
Expected term (in years)	6.25		6.25
Expected volatility	79.83	%	78.18	%
Expected dividend yield	0	%	0	%

Rilonacept Long-Term Incentive Plan

In December 2019, the compensation committee of the Company’s board of directors approved the Company’s Rilonacept Long-Term Incentive Plan (“RLTIP”) under the 2018 Plan to incentivize eligible employees of the Company or any of its subsidiaries to achieve U.S. Food and Drug Administration (“FDA”) approval for the commercial sale and marketing of rilonacept for the treatment of recurrent pericarditis in the United States (“RLTIP Milestone”). The RLTIP provides for the potential to receive a cash award and two grants of restricted share unit (“RSU”) awards covering Class A common shares under the 2018 Plan. The target award value for each of the cash award and the two RSU awards will be equal to one-third of a participant’s annual target bonus for the year of grant, as determined in accordance with the RLTIP.

Depending on the date-range within which the RLTIP Milestone is achieved (such date the “Achievement Date”), the RLTIP provides for (1) an earnout percentage that can be achieved as to 100%, 50%, 25% or 0% and (2) an upside earnout percentage that can be achieved as to 50%, 25% or 0%. No awards will be earned or vest, and the second RSU award will not be granted, in the event the Achievement Date does not occur by a specified date.

The cash award is eligible to be earned and vested upon the Achievement Date with respect to an amount determined in accordance with the RLTIP based on the earnout percentage. The number of Class A common shares issuable under the first RSU award (“First RSU Award”) as a result of the RLTIP Milestone will be determined in accordance with the RLTIP based on the earnout percentage, and such RSUs will vest on the first anniversary of the Achievement Date, subject to continued employment through such date. The second RSU award will be granted on the Achievement Date with respect to a number of shares determined in accordance with the RLTIP, based on both the earnout percentage and the upside earnout percentage, and will vest on the second anniversary of the Achievement Date, subject to continued employment through such date.

Restricted Share Units

An RSU represents the right to receive shares of the Company’s Class A common shares upon vesting of the RSU. The fair value of each RSU is based on the closing price of the Company’s Class A common shares on the date of grant. In December 2019, the Company granted RSUs with service conditions (“Time-Based RSUs”) that vest in one installment on December 31, 2020, subject to the recipient’s continued employment through that date. During the year ended December 31, 2019, the Company also granted the First RSU Award as part of the RLTIP, which becomes eligible to vest upon the Achievement Date and will vest upon the first anniversary of such date, subject to the recipient’s continued employment through that date. In the event the RLTIP Milestone is not achieved, none of the First RSU Award will vest.

The grant-date fair value of the Time-Based RSUs granted in 2019 was $1,250 and will be recognized on a straight-line basis through the vest date for these RSUs. For the three months ended March 31, 2020, the Company recognized $261 in Time-Based RSU expense. The grant-date fair value of the First RSU Award was $2,994 and will be recognized when the RLTIP Milestone is deemed probable of achievement through the date the First RSU Award will vest. During the three months ended March 31, 2020, the Company did not recognize compensation expense related to the First RSU Award, as achievement of the RLTIP Milestone was determined to be not probable.

The following table summarizes RSU activity for the three months ended March 31, 2020:


		Weighted
		Average
	Number of	Grant Date
	Shares	Fair Value
Unvested RSUs as of December 31, 2019	328,296	$	12.93
Granted	—	$	—
Vested	—	$	—
Forfeited	(26,253)	$	12.93
Unvested RSUs as of March 31, 2020	302,043	$	12.93

Share‑Based Compensation

Share‑based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended
	March 31,
	2020		2019
Research and development expenses	$	1,769	$	1,187
General and administrative expenses		2,440		1,706
	$	4,209	$	2,893

Common Shares (Details) $ / shares in Units, $ in Thousands			3 Months Ended
Common Shares (Details) $ / shares in Units, $ in Thousands	Mar. 01, 2019 USD ($) $ / shares shares	Feb. 04, 2019 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) Vote shares	Mar. 31, 2019 USD ($)
Nature of the Business and Basis of Presentation
Common stock, cash dividends declared or paid			$ 0
Common stock, cash dividends paid			0
Preferred stock, cash dividends declared or paid			0
Preferred stock, cash dividends paid			$ 0
Class A common shares
Nature of the Business and Basis of Presentation
Number of votes (per share) \| Vote			1
Class B common shares
Nature of the Business and Basis of Presentation
Number of votes (per share) \| Vote			10
Convertible ratio to Class A common share			1
Convertible ratio to Class B1 common share			1
Class A1 common shares
Nature of the Business and Basis of Presentation
Number of votes (per share) \| Vote			0
Convertible ratio to Class A common share			1
Class B1 common shares
Nature of the Business and Basis of Presentation
Number of votes (per share) \| Vote			0
Convertible ratio to Class A common share			1
Convertible ratio to Class B common share			1
Convertible Preferred Shares (Series A, B and C)
Nature of the Business and Basis of Presentation
Preferred shares designated \| shares			0
Preferred stock, shares issued (in shares) \| shares			0
Over-allotment \| Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) \| shares	161,126
Share price (in dollars per share) \| $ / shares	$ 18.26
Gross proceeds from offering	$ 2,942
Follow-On Public Offering and Private Placement
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs	$ 82,988
Follow-On Public Offering and Private Placement \| Common Class A and Class A1 common shares
Nature of the Business and Basis of Presentation
Gross proceeds from offering		$ 85,000
Follow-On Offering \| Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) \| shares		2,654,984
Share price (in dollars per share) \| $ / shares		$ 18.26
Gross proceeds from offering				$ 48,595
Private Placement \| Class A1 common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) \| shares		2,000,000
Share price (in dollars per share) \| $ / shares		$ 18.26

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Document information
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Entity Registrant Name	Kiniksa Pharmaceuticals, Ltd.
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001730430
Amendment Flag	false
Common Shares
Document information
Entity Common Stock, Shares Outstanding		55,801,712
Class A common shares
Document information
Entity Common Stock, Shares Outstanding		22,285,129
Class B common shares
Document information
Entity Common Stock, Shares Outstanding		2,463,011
Class A1 common shares
Document information
Entity Common Stock, Shares Outstanding		14,995,954
Class B1 common shares
Document information
Entity Common Stock, Shares Outstanding		16,057,618

Fair Value of Financial Assets and Liabilities (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value of Financial Assets and Liabilities

Schedule of financial assets and liabilities measured at fair value on a recurring basis

	Fair Value Measurements
	as of March 31, 2020 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Restricted cash — money market funds	$	210	$	—	$	—	$	210
Cash equivalents — money market funds		54,855		—		—		54,855
Cash equivalents — U.S. Treasury notes		—		42,047		—		42,047
Short-term investments — U.S. Treasury notes		—		97,870		—		97,870
	$	55,065	$	139,917	$	—	$	194,982


	Fair Value Measurements
	as of December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Restricted cash — money market funds	$	210	$	—	$	—	$	210
Cash equivalents — money market funds		25,207		—		—		25,207
Cash equivalents — U.S. Treasury notes		—		10,192		—		10,192
Short-term investments — U.S. Treasury notes		—		186,452		—		186,452
	$	25,417	$	196,644	$	—	$	222,061

Nature of the Business and Basis of Presentation	3 Months Ended
Nature of the Business and Basis of Presentation	Mar. 31, 2020
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Kiniksa Pharmaceuticals, Ltd. (the “Company”) is a biopharmaceutical company focused on discovering, acquiring, developing and commercializing therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. The Company was incorporated in July 2015 as a Bermuda exempted company. The Company has a pipeline of product candidates across various stages of development that are designed to modulate the immunological signaling pathways that are implicated across a spectrum of diseases. The Company is subject to risks and uncertainties common to early‑stage companies in the biopharmaceutical industry and global health, societal, economic and market conditions, including from the impact from the novel coronavirus 2019 (“COVID-19”). There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s technology will be obtained, that any products developed will obtain necessary government regulatory approval or that any products, if approved, will be commercially viable. The Company does not currently generate revenue from sales of any products, and it may never be able to develop or commercialize a marketable product. The Company has not yet successfully completed any Phase 3 or other pivotal clinical trials, obtained any regulatory approvals, manufactured a commercial‑scale drug, or conducted sales and marketing activities. The Company operates in an environment of rapid technological innovation and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, consultants and other third parties, including contract research organizations, or CROs, and contract manufacturing organizations, or CMOs. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Risk and Uncertainties related to COVID-19 In addition to risks and uncertainties common to the Company’s industry, the Company is subject to global societal, healthcare, economic and market conditions, including from the impact of the COVID-19 pandemic, and measures taken in response to the pandemic, which continue to evolve. In December 2019, COVID-19 surfaced in Wuhan, China. The virus spread globally, and was declared a pandemic by the World Health Organization. The impact of this pandemic has been and will likely continue to be extensive on many aspects of society, which has resulted in and will likely continue to result in significant disruptions to healthcare systems, the global economy, as well as businesses and capital markets around the world. In an effort to halt the spread of the COVID-19 pandemic, federal and state governments in the United States and the governments of other countries around the globe have implemented various measures in response to the pandemic, including significant restrictions on businesses and travel as well as social-distancing measures. For example, a number of states, including Massachusetts and California where the Company has offices and laboratory space, have issued shelter-in-place or stay-at-home orders for workers in non-essential businesses. The Company’s business is currently considered to be an essential business so, to date, its operations have only been partially affected by this order, temporarily closing access to its California office space and restricted access to its Massachusetts facility to employees that need to be in the office to execute their responsibilities or who work in its research and development laboratory space, with most of the Company’s employees carrying out their responsibilities outside of the office. The Company is also preparing for any potential re-opening of its offices in Massachusetts and California in the event that the shelter-in-place or stay-at-home orders are lifted. The COVID-19 pandemic, and measures undertaken in response to the pandemic, or the easing of any of such measures, could cause significant disruptions in the Company’s business or operations as well as in the business and operations of the Company’s CMOs, CROs and other third parties with whom the Company conducts business or otherwise engages now or in the future, including as a result of staffing shortages or reprioritizations, production slowdowns or stoppages, and disruptions in delivery systems. The COVID-19 pandemic may also adversely impact the Company’s preclinical studies and clinical trials, which could impede, delay, limit or prevent the clinical development of our product candidates and ultimately lead to the delay or denial of regulatory approval of our product candidates, which would materially adversely affect our business and operations, including our ability to generate revenue. Moreover, the COVID-19 pandemic is impacting the global economy, and the U.S. economy in particular, with the potential for the economic downturn to be severe and prolonged. A severe or prolonged economic downturn could result continued disruptions in the financial markets, which could adversely impact our ability to raise additional capital when needed or on acceptable terms, if at all. While the Company continuously looks to identify business-critical activities and to develop contingencies and mitigation strategies for those activities to potentially minimize the impact of the COVID-19 pandemic on its business and operations, there can be no assurance that it will be able to identify all such activities or that any identified contingencies and mitigation strategies will be effective. Further, the COVID-19 pandemic, and measures undertaken in response to the pandemic continue to rapidly evolve. There is uncertainty relating to the potential effect of the pandemic on the Company’s business and operations. The extent of the impact on the Company’s business and operations will depend on future developments, which are highly uncertain and cannot be predicted with confidence, such as the ultimate spread of the disease, duration of the pandemic, business and travel restrictions and social distancing, and the effectiveness of actions taken to contain and treat the disease. Principles of Consolidation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries, Kiniksa Pharmaceuticals Corp. (“Kiniksa US”), Primatope Therapeutics, Inc. (“Primatope”) and Kiniksa Pharmaceuticals (UK), Ltd. (“Kiniksa UK”) as well as the subsidiaries of Kiniksa UK, Kiniksa Pharmaceuticals (Germany) GmbH (“Kiniksa Germany”) and, Kiniksa Pharmaceuticals (France) SARL (“Kiniksa France”), after elimination of all significant intercompany accounts and transactions. In assessing the consolidation requirement for variable interest entities (“VIE”s), the Company focuses on identifying whether it has both the power to direct the activities that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE. In the event that the Company is the primary beneficiary of a VIE, the assets, liabilities, and results of operations of the VIE would be included in the Company’s consolidated financial statements. At March 31, 2020 and during the three months then ended and at December 31, 2019 and during the year then ended, the Company was not the primary beneficiary of a VIE. Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of common shares and share‑based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Reporting and Functional Currency The financial results of the Company's global activities are reported in U.S. dollars (“USD”) and its foreign subsidiaries generally utilize their respective local currency to be their functional currency. Transactions in other currencies are recorded in the functional currency at the rate of exchange prevailing when the transactions occur. Monetary assets and liabilities denominated in other currencies are re-measured into the functional currency at the rate of exchange in effect at the balance sheet date. Exchange rate gains and losses arising from re-measurement of foreign currency-denominated monetary assets and liabilities are included in income or losses in the period in which they occur. For the Company’s foreign subsidiaries where the local currency is the functional currency, assets and liabilities denominated in local currencies are translated into USD at end-of-period exchange rates and the resulting translation adjustments are reported as a component of accumulated other comprehensive gain (loss) within shareholders' equity. Unaudited Interim Consolidated Financial Information The accompanying unaudited consolidated financial statements have been prepared in accordance with GAAP for interim financial information. The accompanying unaudited consolidated financial statements do not include all of the information and footnotes required by GAAP for complete consolidated financial statements. The accompanying year-end consolidated balance sheet was derived from audited financial statements but does not include all disclosures required by GAAP. The unaudited interim consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2020 and the results of its operations for the three months ended March 31, 2020 and 2019 and its cash flows for the three months ended March 31, 2020 and 2019. The results for the three months ended March 31, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020, any other interim periods or any future year or period. Follow-on Offering and Private Placement On February 4, 2019, the Company completed a follow-on offering of 2,654,984 Class A common shares at a public offering price of $18.26 and a concurrent private placement of 2,000,000 Class A1 common shares at an offering price of $18.26 per share for aggregate gross proceeds of $85,000. In addition, on March 1, 2019, the Company completed the sale of 161,126 Class A common shares to the underwriters of the follow-on offering following the exercise in part of their over-allotment option to purchase additional shares at a public offering price of $18.26 per share for gross proceeds of $2,942. The aggregate net proceeds to the Company from the follow-on offering and concurrent private placement, inclusive of the over-allotment option exercise, was $82,988 after deducting underwriting discounts and commissions and other offering costs Liquidity In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the consolidated financial statements are issued. As of March 31, 2020, the Company had an accumulated deficit of $382,511. During the three months ended March 31, 2020, the Company incurred a net loss of $26,419 and used $31,796 of cash in operating activities. The Company expects to continue to generate operating losses for the foreseeable future. As of March 31, 2020, the Company had cash, cash equivalents and short-term investments of $204,206. Based on its current operating plan, the Company expects that its cash, cash equivalents and short-term investments will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the issuance date of these consolidated financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. The Company will need to finance its operations through public or private securities offerings, debt financings, government funding or grants, or other sources, which may include licensing, collaborations or other strategic transactions or arrangements. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs for product candidates, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations.

Nature of the Business and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Mar. 01, 2019	Feb. 04, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Liquidity
Accumulated deficit			$ 382,511		$ 356,092
Net losses			26,419	$ 65,821
Cash used in operations			31,796	63,256
Cash, cash equivalents and short-term investments			$ 204,206
Over-allotment \| Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)	161,126
Share price (in dollars per share)	$ 18.26
Gross proceeds from offering	$ 2,942
Follow-On Public Offering and Private Placement
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs	$ 82,988
Follow-On Public Offering and Private Placement \| Common Class A and Class A1 common shares
Nature of the Business and Basis of Presentation
Gross proceeds from offering		$ 85,000
Follow-On Offering \| Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)		2,654,984
Share price (in dollars per share)		$ 18.26
Gross proceeds from offering				$ 48,595
Private Placement \| Class A1 common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)		2,000,000
Share price (in dollars per share)		$ 18.26

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses:
Research and development	$ 20,901	$ 59,253
General and administrative	8,486	8,394
Total operating expenses	29,387	67,647
Loss from operations	(29,387)	(67,647)
Interest income	789	1,809
Loss before benefit for income taxes	(28,598)	(65,838)
Benefit for income taxes	2,179	17
Net loss	$ (26,419)	$ (65,821)
Net loss per share attributable to common shareholders—basic and diluted	$ (0.48)	$ (1.27)
Weighted average common shares outstanding—basic and diluted	55,322,690	51,758,353
Comprehensive loss:
Net loss	$ (26,419)	$ (65,821)
Other comprehensive income:
Unrealized gain on short-term investments and currency translation adjustments, net of tax	207	12
Total other comprehensive income	207	12
Total comprehensive loss	$ (26,212)	$ (65,809)

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2020

Summary of Significant Accounting Policies

Principles of Consolidation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries, Kiniksa Pharmaceuticals Corp. (“Kiniksa US”), Primatope Therapeutics, Inc. (“Primatope”) and Kiniksa Pharmaceuticals (UK), Ltd. (“Kiniksa UK”) as well as the subsidiaries of Kiniksa UK, Kiniksa Pharmaceuticals (Germany) GmbH (“Kiniksa Germany”) and, Kiniksa Pharmaceuticals (France) SARL (“Kiniksa France”), after elimination of all significant intercompany accounts and transactions.

In assessing the consolidation requirement for variable interest entities (“VIE”s), the Company focuses on identifying whether it has both the power to direct the activities that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE. In the event that the Company is the primary beneficiary of a VIE, the assets, liabilities, and results of operations of the VIE would be included in the Company’s consolidated financial statements. At March 31, 2020 and during the three months then ended and at December 31, 2019 and during the year then ended, the Company was not the primary beneficiary of a VIE.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of common shares and share‑based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Reporting and Functional Currency

The financial results of the Company's global activities are reported in U.S. dollars (“USD”) and its foreign subsidiaries generally utilize their respective local currency to be their functional currency.

Transactions in other currencies are recorded in the functional currency at the rate of exchange prevailing when the transactions occur. Monetary assets and liabilities denominated in other currencies are re-measured into the functional currency at the rate of exchange in effect at the balance sheet date. Exchange rate gains and losses arising from re-measurement of foreign currency-denominated monetary assets and liabilities are included in income or losses in the period in which they occur.

For the Company’s foreign subsidiaries where the local currency is the functional currency, assets and liabilities denominated in local currencies are translated into USD at end-of-period exchange rates and the resulting translation adjustments are reported as a component of accumulated other comprehensive gain (loss) within shareholders' equity.

Unaudited Interim Consolidated Financial Information

The accompanying unaudited consolidated financial statements have been prepared in accordance with GAAP for interim financial information. The accompanying unaudited consolidated financial statements do not include all of the information and footnotes required by GAAP for complete consolidated financial statements. The accompanying year-end consolidated balance sheet was derived from audited financial statements but does not include all disclosures required by GAAP. The unaudited interim consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2020 and the results of its operations for the three months ended March 31, 2020 and 2019 and its cash flows for the three months ended March 31, 2020 and 2019. The results for the three months ended March 31, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020, any other interim periods or any future year or period.

Cash and Cash Equivalents

Short-Term Investments

Reclassifications

Concentrations of Credit Risk

Restricted Cash

Fair Value Measurements

Level 1—Quoted prices in active markets for identical assets or liabilities.

Leases

Research and Development Costs

Research Contract Costs and Accruals

Share-Based Compensation

Share‑Based Compensation

Comprehensive Loss

Net Loss per Share

Income Taxes

Risk and Uncertainties related to COVID-19

In addition to risks and uncertainties common to the Company’s industry, the Company is subject to global societal, healthcare, economic and market conditions, including from the impact of the COVID-19 pandemic, and measures taken in response to the pandemic, which continue to evolve. In December 2019, COVID-19 surfaced in Wuhan, China. The virus spread globally, and was declared a pandemic by the World Health Organization. The impact of this pandemic has been and will likely continue to be extensive on many aspects of society, which has resulted in and will likely continue to result in significant disruptions to healthcare systems, the global economy, as well as businesses and capital markets around the world.

In an effort to halt the spread of the COVID-19 pandemic, federal and state governments in the United States and the governments of other countries around the globe have implemented various measures in response to the pandemic, including significant restrictions on businesses and travel as well as social-distancing measures. For example, a number of states, including Massachusetts and California where the Company has offices and laboratory space, have issued shelter-in-place or stay-at-home orders for workers in non-essential businesses. The Company’s business is currently considered to be an essential business so, to date, its operations have only been partially affected by this order, temporarily closing access to its California office space and restricted access to its Massachusetts facility to employees that need to be in the office to execute their responsibilities or who work in its research and development laboratory space, with most of the Company’s employees carrying out their responsibilities outside of the office. The Company is also preparing for any potential re-opening of its offices in Massachusetts and California in the event that the shelter-in-place or stay-at-home orders are lifted.

The COVID-19 pandemic, and measures undertaken in response to the pandemic, or the easing of any of such measures, could cause significant disruptions in the Company’s business or operations as well as in the business and operations of the Company’s CMOs, CROs and other third parties with whom the Company conducts business or otherwise engages now or in the future, including as a result of staffing shortages or reprioritizations, production slowdowns or stoppages, and disruptions in delivery systems. The COVID-19 pandemic may also adversely impact the Company’s preclinical studies and clinical trials, which could impede, delay, limit or prevent the clinical development of our product candidates and ultimately lead to the delay or denial of regulatory approval of our product candidates, which would materially adversely affect our business and operations, including our ability to generate revenue. Moreover, the COVID-19 pandemic is impacting the global economy, and the U.S. economy in particular, with the potential for the economic downturn to be severe and prolonged. A severe or prolonged economic downturn could result continued disruptions in the financial markets, which could adversely impact our ability to raise additional capital when needed or on acceptable terms, if at all.

While the Company continuously looks to identify business-critical activities and to develop contingencies and mitigation strategies for those activities to potentially minimize the impact of the COVID-19 pandemic on its business and operations, there can be no assurance that it will be able to identify all such activities or that any identified contingencies and mitigation strategies will be effective. Further, the COVID-19 pandemic, and measures undertaken in response to the pandemic continue to rapidly evolve. There is uncertainty relating to the potential effect of the pandemic on the Company’s business and operations. The extent of the impact on the Company’s business and operations will depend on future developments, which are highly uncertain and cannot be predicted with confidence, such as the ultimate spread of the disease, duration of the pandemic, business and travel restrictions and social distancing, and the effectiveness of actions taken to contain and treat the disease.

Recently Adopted and Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Fair Value of Financial Assets and Liabilities

3 Months Ended

Mar. 31, 2020

Fair Value of Financial Assets and Liabilities

Fair Value of Financial Assets and Liabilities

3. Fair Value of Financial Assets and Liabilities

Short-term investments as of March 31, 2020 and December 31, 2019 consisted of U.S. Treasury notes which investments were each due within six months of such date. As of March 31, 2020 and December 31, 2019, the fair value of short-term investments was $97,870 and $186,452, respectively. As of March 31, 2020, the amortized cost was $97,630 and gross unrealized gain was $240. As of December 31, 2019, the amortized cost was $186,415 and gross unrealized gain was $37.

The following tables present information about the Company’s financial instruments measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values:


	Fair Value Measurements
	as of March 31, 2020 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Restricted cash — money market funds	$	210	$	—	$	—	$	210
Cash equivalents — money market funds		54,855		—		—		54,855
Cash equivalents — U.S. Treasury notes		—		42,047		—		42,047
Short-term investments — U.S. Treasury notes		—		97,870		—		97,870
	$	55,065	$	139,917	$	—	$	194,982


	Fair Value Measurements
	as of December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Restricted cash — money market funds	$	210	$	—	$	—	$	210
Cash equivalents — money market funds		25,207		—		—		25,207
Cash equivalents — U.S. Treasury notes		—		10,192		—		10,192
Short-term investments — U.S. Treasury notes		—		186,452		—		186,452
	$	25,417	$	196,644	$	—	$	222,061

As of March 31, 2019, the Company did not hold any securities that were in an unrealized loss position. As of December 31, 2019, the Company held seven securities that were in an unrealized loss position. The aggregate fair value of securities held by the Company in an unrealized loss position at December 31, 2019 was $43,107. These securities were held by the Company in an unrealized loss position for less than 12 months. The Company determined that there was no material change in the credit risk of these securities. As a result, the Company determined it did not hold any investments with an other-than-temporary impairment as of March 31, 2020 and December 31, 2019.

During the three months ended March 31, 2020 and the year ended December 31, 2019 there were no transfers between Level 1, Level 2 and Level 3. The money market funds were valued using quoted prices in active markets, which represent a Level 1 measurement in the fair value hierarchy. The Company's cash equivalents and short-term investments as of March 31, 2020 and December 31, 2019 included U.S. Treasury notes, which are not traded on a daily basis and, therefore, represent a Level 2 measurement in the fair value hierarchy at each period end.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Fair Value of Financial Assets and Liabilities (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) security
Fair Value, Assets Transfers
Fair value of assets transferred from Level 1 to Level 2	$ 0	$ 0
Fair value of assets transferred from Level 2 to Level 1	0	0
Fair value of assets transferred from Level 1 to Level 3	0	0
Fair value of assets transferred from Level 2 to Level 3	0	0
Fair value of assets transferred from Level 3 to Level 1	0	0
Fair value of assets transferred from Level 3 to Level 2	0	$ 0
Number of securities \| security		7
Unrealized loss position		$ 43,107
U.S. Treasury Notes
Assets
Amortized cost of short-term investments	97,630	186,415
Unrealized gain on short-term investments	240	37
Short-term investments	97,870	186,452
Fair Value \| Recurring basis
Assets
Assets	194,982	222,061
Fair Value \| Recurring basis \| Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	54,855	25,207
Fair Value \| Recurring basis \| U.S. Treasury Notes
Assets
Cash equivalents	42,047	10,192
Short-term investments	97,870	186,452
Fair Value \| Recurring basis \| Level 1
Assets
Assets	55,065	25,417
Fair Value \| Recurring basis \| Level 1 \| Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	54,855	25,207
Fair Value \| Recurring basis \| Level 2
Assets
Assets	139,917	196,644
Fair Value \| Recurring basis \| Level 2 \| U.S. Treasury Notes
Assets
Cash equivalents	42,047	10,192
Short-term investments	$ 97,870	$ 186,452

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (26,419)	$ (65,821)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	594	471
Share-based compensation expense	4,209	2,893
Class A common shares issued or to be issued as consideration for Primatope, including milestone payments		7,000
Non-cash lease expense	300	334
Accretion of discounts on short-term investments	(228)	(846)
Deferred income taxes	(1,038)	(240)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(598)	(1,544)
Accounts payable	(1,197)	(3,343)
Accrued expenses and other liabilities	(7,061)	(376)
Accrued milestones		(2,000)
Operating lease liabilities	(413)	(293)
Other long-term liabilities	55	509
Net cash used in operating activities	(31,796)	(63,256)
Cash flows from investing activities:
Purchases of property and equipment	(223)	(1,561)
Purchases of short-term investments	(26,187)	(181,807)
Proceeds from the maturities of short-term investments	115,200	174,090
Net cash provided by (used in) investing activities	88,790	(9,278)
Cash flows from financing activities:
Payments of offering costs		(100)
Proceeds from exercise of options and employee share purchase plan	2,414	181
Net cash provided by financing activities	2,414	83,187
Net increase in cash, cash equivalents and restricted cash	59,408	10,653
Cash, cash equivalents and restricted cash at beginning of period	47,138	72,186
Cash, cash equivalents and restricted cash at end of period	$ 106,546	82,839
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accrued expenses and accounts payable		19
Property and equipment included in accrued expenses and accounts payable		37
Follow-On Offering \| Class A common shares
Cash flows from financing activities:
Proceeds from issuance of common shares, net of underwriting commissions and discounts		48,595
Private Placement \| Class A1 common shares
Cash flows from financing activities:
Proceeds from issuance of common shares from private placement, net of underwriting commissions and discounts		$ 34,511

Share-Based Compensation - Options (Details) - Class A common shares - Stock options	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of Shares
Outstanding, beginning of the period \| shares	8,491,734
Granted \| shares	1,455,250
Exercised \| shares	(643,867)
Forfeited \| shares	(234,919)
Cancelled \| shares	(77,326)
Outstanding, end of the period \| shares	8,990,872
Options exercisable \| shares	3,176,450
Options unvested \| shares	5,814,422
Weighted Average Grant Date Fair Value
Outstanding, beginning of the period \| $ / shares	$ 7.68
Granted \| $ / shares	10.74
Exercised \| $ / shares	2.50
Forfeited \| $ / shares	10.89
Cancelled \| $ / shares	16.72
Outstanding, end of the period \| $ / shares	8.39
Options exercisable \| $ / shares	8.26
Options unvested \| $ / shares	$ 9.63

Net Loss per Share - Anti-Dilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	9,292,915	7,805,094
Stock options
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	8,990,872	7,195,501
Restricted shares
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share		609,593
Restricted Share Units (RSUs)
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	302,043

License and Acquisition Agreements - Regeneron License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Sep. 30, 2017	Mar. 31, 2020	Mar. 31, 2019
License and Acquisition Agreements
Research and development		$ 20,901	$ 59,253
Regeneron \| License Agreement
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 5,000
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured	90 days
Research and development		0	0
Notice period to terminate the agreement under payment-related breaches	30 days
Consecutive suspension of activities period for termination of agreement	12 months
Period after which the agreement can be terminated	18 months
Notice period to terminate the agreement	180 days
Notice period to terminate the agreement after US marketing approval of the developed product	1 year
Notice period to terminate the agreement if products are having safety concerns	3 months
Regeneron \| Clinical Supply Agreement
License and Acquisition Agreements
Research and development expense related to purchase of drug materials		$ 0	$ 515
Maximum \| Regeneron \| License Agreement
License and Acquisition Agreements
Milestone payment to be paid upon regulatory milestone achievement	$ 27,500

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Income Taxes
Bermuda statutory income tax rate	0.00%
Income tax benefits - Bermuda	$ 0	$ 0
Net operating loss carryforwards - Bermuda	0	0
Benefit for income taxes	2,179	$ 17
Discrete tax benefit	1,828
Deferred tax asset	$ 5,410

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2020
Commitments and Contingencies
Commitments and Contingencies	12. Commitments and Contingencies License Agreements The Company entered into license agreements with various parties under which it is obligated to make contingent and non‑contingent payments (see Note 9). Manufacturing Commitments The Company entered into agreements with several contract manufacturing organizations to provide preclinical and clinical trial materials. As of March 31, 2020, the Company had committed to minimum payments under these agreements totaling $1,508. Rilonacept Long-Term Incentive Plan During the year ended December 31, 2019, the Company granted a cash award and the First RSU Award to employees under the RLTIP. The cash award vests upon the achievement of the RLTIP Milestone, subject to the recipient’s continued employment. The First RSU Award becomes eligible to vest upon the achievement of the RLTIP Milestone, and will vest upon the first anniversary of such date, subject to the recipient’s continued employment through that date. As of March 31, 2020, the Company estimated cash payments of $1,938 under the RLTIP. In the event the RLTIP Milestone is not achieved, the cash award will not be paid and the First RSU Award will not vest. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors, officers and other key personnel that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or other key personnel. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of March 31, 2020 or December 31, 2019. Legal Proceedings The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities.

Common Shares	3 Months Ended
Common Shares	Mar. 31, 2020
Common Shares.
Common Shares	7. Common Shares On February 4, 2019, the Company completed a follow-on offering of 2,654,984 Class A common shares at a public offering price of $18.26 and a concurrent private placement of 2,000,000 Class A1 common shares at an offering price of $18.26 per share for aggregate gross proceeds of $85,000. In addition, on March 1, 2019, the Company completed the sale of 161,126 Class A common shares to the underwriters of the follow-on offering following the exercise in part of their over-allotment option to purchase additional shares at a public offering price of $18.26 per share for gross proceeds of $2,942. The aggregate net proceeds to the Company from the follow-on offering and concurrent private placement, inclusive of the over-allotment option exercise, was $82,988 after deducting underwriting discounts and commissions and other offering costs. The rights of the holders of the Company’s Class A common shares, Class B common shares, Class A1 common shares and Class B1 common shares are identical, except with respect to voting, transferability and conversion, as described below. As of March 31, 2020, no preferred shares were designated or issued. Voting Each Class A common share entitles the holder to one vote on all matters submitted to the shareholders for a vote. Each Class B common share entitles the holder to ten votes on all matters submitted to the shareholders for a vote. The holders of Class A and Class B common shares, voting together as a single class, are entitled to elect the directors of the Company. Holders of Class A1 common shares and Class B1 common shares have no voting rights. Dividends Common shareholders are entitled to receive dividends, as may be declared by the Company’s board of directors. Through March 31, 2020, no cash dividends have been declared or paid. Conversion Each Class B common share shall automatically convert into one Class A common share upon certain transfers of such shares by the holder thereof (subject to certain exceptions). Each Class B common share is convertible, at the holder’s election into one Class A common share or one Class B1 common share. Each Class A1 common share is convertible into one Class A common share at the holder’s election (subject to certain exceptions). Each Class B1 common share shall automatically convert into one Class A common share upon certain transfers of such shares by the holder thereof (subject to certain exceptions). Each Class B1 common share is convertible into one Class A common share or one Class B common share at the holder’s election (subject to certain exceptions). There are no conversion rights associated with the Class A common shares.

Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss attributable to common shareholders	$ (26,419)	$ (65,821)
Denominator:
Weighted average common shares outstanding — basic and diluted	55,322,690	51,758,353
Net loss per share attributable to common shareholders — basic and diluted	$ (0.48)	$ (1.27)

License and Acquisition Agreements - Novo Nordisk License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Aug. 31, 2017	Mar. 31, 2020	Mar. 31, 2019
License and Acquisition Agreements
Research and development		$ 20,901	$ 59,253
License Agreement \| Novo Nordisk
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 1,500
Research and development		$ 0	$ 0

Leases - Operating Leases (Details) $ in Thousands		1 Months Ended	3 Months Ended
Leases - Operating Leases (Details) $ in Thousands	Dec. 21, 2018 USD ($) ft²	Dec. 31, 2019 USD ($)	Mar. 31, 2020	Nov. 07, 2018 ft²	Jun. 26, 2018 ft²
Maximum
Operating leases
Remaining lease terms			2 years
Lexington office
Operating leases
Area of leased space after expansion \| ft²				55,924	27,244
Monthly base rent payment \| $		$ 138
San Diego office
Operating leases
Area of leased space after expansion \| ft²	4,400
Monthly base rent payment \| $	$ 13

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Class A common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	21,519,500	19,245,201
Common stock, shares outstanding (in shares)	21,519,500	19,245,201
Class B common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	3,008,373	4,638,855
Common stock, shares outstanding (in shares)	3,008,373	4,638,855
Class A1 common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	14,995,954	14,995,954
Common stock, shares outstanding (in shares)	14,995,954	14,995,954
Class B1 common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	16,057,618	16,057,618
Common stock, shares outstanding (in shares)	16,057,618	16,057,618

Share-Based Compensation - Restricted Shares and RSUs (Details) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) installment $ / shares shares
Share-based compensation
Share-based compensation expense	$ 4,209	$ 2,893
Restricted Share Units (RSUs)
Number of shares
Beginning of the period \| shares	328,296
Forfeited \| shares	(26,253)
End of the period \| shares	302,043		328,296
Weighted Average Fair Value at Issuance
Beginning of the period \| $ / shares	$ 12.93
Forfeited \| $ / shares	12.93
End of the period \| $ / shares	$ 12.93		$ 12.93
Time-based RSUs
Share-based compensation
Number of vesting installments \| installment			1
Grant date fair value awards granted			$ 1,250
Share-based compensation expense	$ 261
First RSU Award
Share-based compensation
Number of awards that will vest in the event performance goals are not achieved \| shares			0
Grant date fair value awards granted	2,994
Share-based compensation expense	$ 0

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Expenses
Accrued research and development expenses	$ 8,479	$ 11,813
Accrued employee compensation and benefits	3,456	7,089
Accrued legal and professional fees	726	1,087
Other	718	426
Accrued expenses	$ 13,379	$ 20,415

License and Acquisition Agreements - MedImmune License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Research and development		$ 20,901	$ 59,253
MedImmune \| License Agreement
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 8,000
Milestone payment to be paid upon regulatory milestone achievement	10,000
Accrued milestone payments	10,000				$ 5,000
Payment of accrued milestones				$ 10,000
Pass-through payment paid upon clinical milestone achievement				$ 5,000
Annual net sales excluded from calculation of specified annual net sales thresholds	$ 1,000,000
Maximum percentage of royalty payable on annual net sales of licensed products	20.00%
Notice period to terminate the agreement by both parties for material breaches	90 days
Notice period to terminate the agreement	90 days
Research and development		$ 0	$ 0
Minimum \| MedImmune \| License Agreement
License and Acquisition Agreements
Additional specified annual net sales threshold for additional milestone payment.	$ 1,000,000
Maximum \| MedImmune \| License Agreement
License and Acquisition Agreements
Milestone payment to be paid upon specified milestone achievements for first two indications	72,500
Milestone payment to be paid upon clinical and regulatory milestone achievement	15,000
Milestone payment to be paid upon specified annual sales milestone achievements	85,000
Additional milestone payments payable after achievement of additional annual sales	$ 1,100,000

Summary of Significant Accounting Policies - Concentrations of Credit Risk and Restricted Cash (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($) item
Restricted cash
Cash securing letter of credit \| $	$ 210	$ 210
Cash and cash equivalents \| Credit concentration
Concentration risk
Number of financial institutions holding cash, cash equivalents and short-term investments \| item	2	2

License and Acquisition Agreements - Biogen Asset Purchase Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 30, 2016	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2017
License and Acquisition Agreements
Research and development		$ 20,901	$ 59,253
Asset Purchase Agreement \| Biogen
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 11,500
Technology transfer payment	500
Milestone payment upon achievement of clinical milestone event		0		$ 10,000	$ 4,000
One-time payment of upfront sublicense fee on retained contracts	150
Maximum aggregate obligation to pay insignificant annual maintenance fees as well as clinical and regulatory milestone payments	$ 1,575
Notice period to terminate the agreement	90 days
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured	90 days
Notice period to terminate the agreement under payment-related breaches	30 days
Research and development		$ 64	$ 10,002
Asset Purchase Agreement \| Biogen \| Maximum
License and Acquisition Agreements
Milestone payment to be paid upon clinical and regulatory milestone achievement	$ 179,000
Milestone payment to be paid upon net sales milestone achievement	$ 150,000

Leases - Lease Cost and Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease cost
Operating lease cost	$ 340	$ 401
Variable lease cost	$ 50	$ 22
Weighted average lease term	1 year 2 months 19 days
Discount rate	7.16%
Maturities of operating lease liabilities
2020	$ 1,366
2021	972
Total future minimum lease payments	2,338
Less imputed interest	(98)
Present value of lease liabilities	$ 2,240

License and Acquisition Agreements - Primatope Stock Purchase Option Agreement (Details) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Sep. 30, 2017 USD ($) item	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)
License and Acquisition Agreements
Research and development			$ 20,901	$ 59,253
Primatope \| Stock Option Purchase Agreement
License and Acquisition Agreements
Percentage of capital stock available to purchase in call option		100.00%
Payment for extension of option period					$ 800
Primatope Acquisition
License and Acquisition Agreements
Purchase price	$ 18,000
Upfront consideration payable on exercise of call option to acquire all outstanding equity	10,000			10,000
Milestone payment payable after achievement of specified milestones	$ 5,000			5,000		$ 3,000
Research and development				$ 18,000
Primatope Acquisition \| Stock Option Purchase Agreement
License and Acquisition Agreements
Upfront payment for initial option period		$ 500
Maximum \| Primatope \| Stock Option Purchase Agreement
License and Acquisition Agreements
Number of extensions allowed for initial option period \| item		3
Total aggregate extension payments		$ 800

Commitments and Contingencies (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Manufacturing commitments
Non-cancelable purchase commitments	$ 1,508
Rilonacept Long-term Incentive Plan \| First RSU Award
Long-term incentive plan
Estimated amount of cash award in the event performance goals are achieved	$ 1,938

Share-Based Compensation - Option Valuation (Details)	3 Months Ended
Share-Based Compensation - Option Valuation (Details)	Mar. 31, 2020	Mar. 31, 2019
Assumptions to determine fair value of options granted on weighted average basis:
Risk-free interest rate	0.82%	2.58%
Expected term (in years)	6 years 3 months	6 years 3 months
Expected volatility	79.83%	78.18%
Expected dividend yield	0.00%	0.00%