Prothena (PRTA) 10-K 22 Feb 24 2023 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2023	Feb. 15, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-35676
Entity Registrant Name	PROTHENA CORPORATION PUBLIC LIMITED COMPANY
Entity Incorporation, State or Country Code	L2
Entity Tax Identification Number	98-1111119
Entity Address, Address Line One	77 Sir John Rogerson’s Quay, Block C
Entity Address, Address Line Two	Grand Canal Docklands
Entity Address, City or Town	Dublin 2,
Entity Address, Postal Zip Code	D02 VK60,
Entity Address, Country	IE
Country Region	353
City Area Code	1
Local Phone Number	236-2500
Title of 12(b) Security	Ordinary Shares, par value $0.01 per share
Trading Symbol	PRTA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 2,900,000,000
Entity Ordinary Shares Outstanding		53,720,455
Documents Incorporated by Reference	Portions of the registrant’s Proxy Statement to be delivered to shareholders in connection with the registrant’s Annual General Meeting of Shareholders to be held on May 14, 2024, are incorporated by reference into Part III of this Form 10-K. The registrant intends to file its Proxy Statement within 120 days after its fiscal year ended December 31, 2023.
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Central Index Key	0001559053

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Name	KPMG LLP
Auditor Location	San Francisco, CA
Auditor Firm ID	185

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 618,830	$ 710,406
Accounts receivable	5,159	0
Prepaid expenses and other current assets	13,941	8,692
Restricted cash, current	1,352	0
Total current assets	639,282	719,098
Non-current assets:
Property and equipment, net	3,836	1,731
Operating lease right-of-use assets	12,162	6,277
Deferred tax assets	33,893	18,204
Restricted cash, non-current	860	2,212
Other non-current assets	6,349	10,513
Total non-current assets	57,100	38,937
Total assets	696,382	758,035
Current liabilities:
Accounts payable	25,391	9,270
Accrued research and development	14,724	10,794
Deferred revenue, current	0	11,442
Lease liability, current	1,114	6,473
Other current liabilities	15,662	12,168
Total current liabilities	56,891	50,147
Non-current liabilities:
Deferred revenue, non-current	67,405	85,293
Lease liability, non-current	10,721	0
Other liabilities	0	553
Total non-current liabilities	78,126	85,846
Total liabilities	135,017	135,993
Commitments and contingencies (Note 6)
Shareholders’ equity:
Euro deferred shares, €22 nominal value: Authorized shares — 10,000 at December 31, 2023 and 2022 Issued and outstanding shares — none at December 31, 2023 and 2022	0	0
Ordinary shares, $0.01 par value: Authorized shares — 100,000,000 at December 31, 2023 and 2022 Issued and outstanding shares — 53,682,117 and 52,103,608 at December 31, 2023 and 2022, respectively	537	521
Additional paid-in capital	1,540,859	1,454,524
Accumulated deficit	(980,031)	(833,003)
Total shareholders’ equity	561,365	622,042
Total liabilities and shareholders’ equity	$ 696,382	$ 758,035

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical)	Dec. 31, 2023 € / shares shares	Dec. 31, 2023 $ / shares shares	Dec. 31, 2022 € / shares shares	Dec. 31, 2022 $ / shares shares
Statement of Financial Position [Abstract]
Euro deferred shares, nominal value (in euros per share) | € / shares	€ 22		€ 22
Euro deferred shares, number of shares authorized (in shares)	10,000	10,000	10,000	10,000
Euro deferred shares, number of issued shares (in shares)	0	0	0	0
Euro deferred shares, number of outstanding shares (in shares)	0	0	0	0
Ordinary shares, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Ordinary shares, number of authorized shares (in shares)	100,000,000	100,000,000	100,000,000	100,000,000
Ordinary shares, number of issued shares (in shares)	53,682,117	53,682,117	52,103,608	52,103,608
Ordinary shares, number of outstanding shares (in shares)	53,682,117	53,682,117	52,103,608	52,103,608

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues	$ 91,370	$ 53,905	$ 200,577
Operating expenses:
Research and development	220,571	135,562	82,284
General and administrative	61,835	49,900	46,318
Total operating expenses	282,406	185,462	128,602
Income (loss) from operations	(191,036)	(131,557)	71,975
Other income (expense):
Interest income	31,014	6,349	42
Other expense, net	(458)	(397)	(96)
Total other income (expense), net	30,556	5,952	(54)
Income (loss) before income taxes	(160,480)	(125,605)	71,921
Provision for (benefit from) income taxes	(13,452)	(8,656)	4,946
Net income (loss)	$ (147,028)	$ (116,949)	$ 66,975
Earnings Per Share, Basic	$ (2.76)	$ (2.47)	$ 1.51
Earnings Per Share, Diluted	$ (2.76)	$ (2.47)	$ 1.38
Weighted Average Number of Shares Outstanding, Basic	53,216	47,369	44,228
Weighted Average Number of Shares Outstanding, Diluted	53,216	47,369	48,464
Collaboration revenue
Revenues	$ 91,320	$ 13,855	$ 139,833
Revenue from license and intellectual property
Revenues	$ 50	$ 40,050	$ 60,744

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net income (loss)	$ (147,028)	$ (116,949)	$ 66,975
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Depreciation and amortization	928	744	1,115
Share-based compensation	40,914	31,322	24,658
Deferred income taxes	(15,689)	(11,133)	4,573
Reduction in the carrying amount of right-of-use assets	7,484	5,997	5,688
Loss on disposal of fixed assets	15	1	0
Changes in operating assets and liabilities:
Accounts receivable	(5,159)	0	15
Prepaid expenses and other assets	(2,537)	(10,809)	(4,763)
Deferred revenue	(29,330)	(13,855)	348
Accounts payable, accruals and other liabilities	22,855	11,865	(492)
Operating lease liabilities	(6,359)	(6,004)	(5,512)
Net cash provided by (used in) operating activities	(133,906)	(108,821)	92,605
Investing activities
Purchases of property and equipment	(2,810)	(464)	(575)
Proceeds from disposal of fixed assets	37	0	0
Net cash used in investing activities	(2,773)	(464)	(575)
Financing activities
Proceeds from issuance of ordinary shares upon exercise of stock options	21,520	17,841	15,544
Net cash provided by financing activities	45,103	241,457	190,332
Net increase (decrease) in cash, cash equivalents and restricted cash	(91,576)	132,172	282,362
Cash, cash equivalents and restricted cash, beginning of the year	712,618	580,446	298,084
Cash, cash equivalents and restricted cash, end of the period	621,042	712,618	580,446
Supplemental disclosures of cash flow information
Cash paid for income taxes, net	1,554	2,659	580
Supplemental disclosures of non-cash investing and financing activities
Receivable from option exercises	0	62	13
Acquisition of property and equipment included in accounts payable and accrued liabilities	237	0	0
Right-of-use assets obtained in exchange for lease obligations	3,810	151	0
Reclassification of prepaid lease payments to right-of-use assets upon lease commencement	7,763	0	0
Cash and cash equivalents	618,830	710,406	579,094
Restricted cash, current	1,352	0	0
Restricted cash, non-current	860	2,212	1,352
Total cash, cash equivalents and restricted cash, end of the period	621,042	712,618	580,446
Public Offering
Financing activities
Proceeds from issuance of ordinary shares in public offering, net	20,689	172,583	78,049
Supplemental disclosures of non-cash investing and financing activities
Offering Costs Included In Accounts Payable And Accrued Liabilities	0	220	0
At-The-Market Offering
Financing activities
Proceeds from issuance of ordinary shares in at-the market offering, net	2,894	51,033	96,739
Supplemental disclosures of non-cash investing and financing activities
Offering Costs Included In Accounts Payable And Accrued Liabilities	$ 6	$ 13	$ 0

Consolidated Statement of Share

Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Public Offering	At-The-Market Offering	Ordinary Shares	Ordinary Shares Public Offering	Ordinary Shares At-The-Market Offering	Additional Paid-in Capital	Additional Paid-in Capital Public Offering	Additional Paid-in Capital At-The-Market Offering	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020				39,921,413
Beginning balance, value at Dec. 31, 2020	$ 184,006			$ 399			$ 966,636			$ (783,029)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-Based Compensation	24,658						24,658
Issuance of ordinary shares upon exercise of stock options (in shares)				1,073,707
Issuance of ordinary shares upon exercise of stock options	15,557			$ 11			15,546
Issuance of ordinary shares (in shares)					4,025,000	1,640,174
Proceeds from issuance of ordinary shares in public offering, net		$ 78,049	$ 96,797		$ 40	$ 16		$ 78,009	$ 96,781
Net income (loss)	66,975									66,975
Ending balance (in shares) at Dec. 31, 2021				46,660,294
Ending balance, value at Dec. 31, 2021	466,042			$ 466			1,181,630			(716,054)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-Based Compensation	31,322						31,322
Issuance of ordinary shares upon exercise of stock options (in shares)				1,282,086
Issuance of ordinary shares upon exercise of stock options	17,890			$ 14			17,876
Issuance of ordinary shares (in shares)					3,250,000	911,228
Proceeds from issuance of ordinary shares in public offering, net		172,363	51,374		$ 32	$ 9		172,331	51,365
Net income (loss)	(116,949)									(116,949)
Ending balance (in shares) at Dec. 31, 2022				52,103,608
Ending balance, value at Dec. 31, 2022	622,042			$ 521			1,454,524			(833,003)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-Based Compensation	$ 40,914						40,914
Issuance of ordinary shares upon exercise of stock options (in shares)	1,135,302			1,135,302
Issuance of ordinary shares upon exercise of stock options	$ 21,457			$ 12			21,445
Issuance of ordinary shares (in shares)					395,096	42,361
Proceeds from issuance of ordinary shares in public offering, net		$ 20,909	$ 3,071		$ 4	$ 0		$ 20,905	$ 3,071
Issuance of ordinary shares upon vesting of restricted stock units (in shares)				5,750
Issuance of ordinary shares upon vesting of restricted stock units	0			$ 0			0
Net income (loss)	(147,028)									(147,028)
Ending balance (in shares) at Dec. 31, 2023				53,682,117
Ending balance, value at Dec. 31, 2023	$ 561,365			$ 537			$ 1,540,859			$ (980,031)

Consolidated Statement of Sha_2

Consolidated Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Public Offering
Stock Issuance Costs	$ (1,400)	$ (11,300)	$ (5,500)
At-The-Market Offering
Stock Issuance Costs	$ (153)	$ (1,700)	$ (3,200)

Organization

Organization	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Description of Business Prothena Corporation plc (“Prothena” or the “Company”) is a late-stage clinical biotechnology company with expertise in protein dysregulation and a pipeline of investigational therapeutics with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases. Fueled by its deep scientific expertise built over decades of research, the Company is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. The Company’s wholly-owned programs include birtamimab for the potential treatment of AL amyloidosis, and a portfolio of programs for the potential treatment of Alzheimer’s disease including PRX012, which targets amyloid beta (Aβ), and PRX123, a novel dual Aβ-tau vaccine. The Company’s partnered programs include prasinezumab, in collaboration with Roche for the potential treatment of Parkinson’s disease and other related synucleinopathies, and programs that target tau (BMS-986446, formerly PRX005), TDP-43, and an undisclosed target (PRX019) in collaboration with Bristol Myers Squibb (BMS) for the potential treatment of Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases, respectively. The Company is also entitled to certain potential milestone payments pursuant to the Company’s share purchase agreement with Novo Nordisk pertaining to the Company’s ATTR amyloidosis business (including NNC6019, formerly PRX004). The Company was formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market. Liquidity and Business Risks As of December 31, 2023, the Company had an accumulated deficit of $980.0 million and cash and cash equivalents of $618.8 million. Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at December 31, 2023, are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. The Company expects to continue to finance future cash needs that exceed its cash from operating activities primarily through its current cash and cash equivalents, payments pursuant to its agreements with Roche, BMS, and Novo Nordisk, and, to the extent necessary, through proceeds from public or private equity or debt financings, loans and other collaborative agreements with corporate partners or other arrangements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Preparation and Presentation of Financial Information These Consolidated Financial Statements have been prepared in accordance with the accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). These Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Consolidated Financial Statements of Prothena Corporation plc are presented in U.S. dollars, which is the functional currency of the Company and its consolidated subsidiaries. Monetary assets and liabilities denominated in foreign currency are remeasured at period-end exchange rates. Foreign currency gains and losses resulting from remeasurement are recognized in other expense, net in the Consolidated Statements of Operations. Use of Estimates The preparation of the Consolidated Financial Statements in conformity with U.S. GAAP requires the Company to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures. On an ongoing basis, management evaluates its estimates, including critical accounting policies or estimates related to revenue recognition and research and development expenses. Th e Company bases its estimates on historical experience and on various other market specific and other relevant assumptions that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates. Significant Accounting Policies Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments held at financial institutions, such as commercial paper, money market funds, and other money market securities with original maturities of three months or less at date of purchase to be cash equivalents. Cash accounts that are restricted to withdrawal or usage are presented as restricted cash. As of December 31, 2023, the Company had $2.2 million of restricted cash held by a bank in certificates of deposit as collateral to standby letters of credit under certain operating leases. See Note 6, "Commitments and Contingencies" for additional information regarding the Company’s operating leases. Accounts Receivable The accounts receivable balance on the Consolidated Balance Sheets represents amounts receivable from the Company's collaboration partners. The Company monitors the financial performance and creditworthiness of customers so that it can properly assess and respond to changes in their credit profiles. The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for credit losses against the trade account receivables, when appropriate. As of December 31, 2023, the Company has not provided any allowance for credit losses against its outstanding accounts receivables. Property and Equipment, net Property and equipment, net are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the related assets. Maintenance and repairs are charged to expense as incurred, and leasehold improvements where the Company is deemed the accounting owner are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized. Depreciation and amortization periods for the Company’s property, plant and equipment are as follows: Asset Estimated Useful Life Machinery and equipment 4-7 years Leasehold improvements Shorter of expected useful life or lease term Purchased computer software 4 years Impairment of Long-lived Assets The Company periodically evaluates property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable or the estimated useful life is no longer appropriate. If such events or changes in circumstances arise, the Company compares the carrying amount of the asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of the long-lived asset is not recoverable on an undiscounted cash flow basis, an impairment charge is recognized to the extent that the carrying amount exceeds its fair value. The Company determines fair value using the income approach based on the present value of expected future cash flows. The Company’s cash flow assumptions consider historical and forecasted revenue and operating costs and other relevant factors. There were no impairment charges recorded during the years ended December 31, 2023, 2022 and 2021. See Note 4, “Composition of Certain Balance Sheet Items” for discussion on disposals. Leases The Company leases both real property and certain equipment for use in its operations. A determination is made as to whether an arrangement is a lease at inception. If so, the Company evaluates the lease agreement to determine whether the lease is an operating or finance lease using the criteria in ASC 842. The Company does not recognize right-of-use assets and lease liabilities that arise from short-term leases for any class of underlying assets. When lease agreements also require the Company to make additional payments for taxes, insurance and other operating expenses incurred during the lease period, such payments are expensed as incurred. See Note 6, “Commitments and Contingencies,” which provides additional details on the Company's current lease arrangements. As of December 31, 2023 and 2022, the Company had no financing leases. Operating leases are included in the operating lease right-of-use (“ROU”) assets, lease liability, current and lease liability, non-current in the Company's Consolidated Balance Sheets. Operating lease ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of all lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on information available at the lease commencement date. The operating lease ROU assets also include any lease prepayments made and exclude lease incentives such as rent abatements and/or concessions and rent holidays. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed by management to be reasonably certain at lease inception. Tenant improvements made by the Company as a lessee in which they are deemed to be owned by the lessor is viewed as lease prepayments by the Company and included in the operating lease ROU assets upon commencement of the lease prior to which they are recorded as prepaid assets. Lease expense for operating leases is recognized on a straight-line basis over the expected lease term as an operating expense. For lease agreements that include lease and non-lease components, such components are generally accounted for separately. Revenue Recognition The Company’s collaboration revenue includes revenue recognized for milestone payments and reimbursements under the Company’s License Agreement with Roche as well as revenue recognized under the Company’s Collaboration Agreement with BMS. The Company’s l icense and intellectual property revenue includes revenue from Novo Nordisk for the sale of intellectual property and related rights to the Company’s ATTR amyloidosis business and pipeline and milestones payments. The Company analyzes its collaboration arrangements to assess whether they are financing arrangement within the scope of ASC 730 or as a collaboration arrangement pursuant to ASC 808, or whether such arrangements are reflective of a vendor-customer relationship and therefore within the scope of Topic 606. As of December 31, 2023, t he Company has not had any arrangements outside the scope of Topic 606. The following describes the Company’s accounting treatment pursuant to Topic 606: License, Option and Collaboration Revenue The terms of license, option and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front license fees; option exercise fees; development, regulatory and commercial milestone payments; payments for manufacturing supply and research and development services and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities recorded as deferred revenue in the Company’s Consolidated Balance Sheets. At contract inception, for contracts that contain multiple performance obligations, such as the Company’s License Agreement with Roche and the Collaboration Agreement with BMS, the Company accounts for the individual performance obligations separately if they are distinct. Factors considered in the determination of whether the license performance obligations are distinct included, among other things, the research and development capabilities of each of Roche and BMS and their respective sublicense rights, and for the remaining performance obligations the fact that they are not proprietary and can be and have been provided by other vendors. The transaction price is allocated to the separate performance obligation on a relative standalone selling price basis. Revenue is recognized only when the Company satisfies an identified performance obligation by transferring a promised good or service to a customer (in th e Compan y’s case, Roche and BMS). An asset is transferred when, or as, the customer obtains control of that asset, which for a service is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. Milestone Revenue The Company generally classifies each of its milestones into one of three categories: (i) clinical milestones; (ii) regulatory and development milestones; and (iii) commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research. For example, a milestone payment may be due to the Company upon the initiation of a clinical trial for a new indication. Regulatory and development milestones are typically achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the FDA or other regulatory authorities. For example, a milestone payment may be due to the Company upon submission for marketing approval of a product candidate by the FDA. Commercial milestones are typically achieved when an approved product reaches certain defined levels of net royalty sales by the licensee of a specified amount within a specified period. At the inception of each arrangement that includes developmental, regulatory or commercial milestone payments, the Company evaluates whether achieving the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone (such as a regulatory submission by the Company) is included in the transaction price. Milestone payments that are not within the control of the Company, such as approvals from regulators or where attainment of the specified event is dependent on the development activities of a third party, are not considered probable of being achieved until those approvals are received or the specified event occurs. The Company considers such milestone payments as variable consideration with constraint and therefore recognizes the revenue from such milestone payments as collaboration revenue at point in time when the Company can conclude it is probable that a significant revenue reversal will not occur in future periods. Taxes, Shipping and Handling The Company excludes from the measurement of the transaction price all taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction and collected by the Company from a customer (e.g., sales, use, value added, some excise taxes). In addition, the Company accounts for shipping and handling as activities that are performed after its customers obtain control of the goods as activities to fulfill our performance obligation to transfer the goods. Research and Development Research and development costs are expensed as incurred. Such costs include, but are not limited to, salaries and benefits, share-based compensation, costs related to preclinical and clinical trial activities including fees paid to clinical research organizations and investigative sites, costs related to drug development and manufacturing prior to regulatory approval for commercial sale, and consulting fees. There can be judgment involved in measuring the research and development expenses to be recognized in a particular period. The level of judgment varies based on the nature of the services being performed and the underlying support obtained. The Company recognizes costs for certain development activities, such as clinical trials, based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by our vendors on their actual costs incurred. For certain clinical trials, expense is recorded based on information obtained from vendors as an intermediary to those performing the underlying services, such as contract research organizations. These estimates are inherently more judgmental because the quality and availability of the underlying data may vary. The Company recognizes costs for contract manufacturing based on evaluation of the progress to completion of specific tasks. The objective of the Company’s accrual policy is to match the recording of the expenses in the Consolidated Financial Statements to the actual services the Company has received and efforts expended. As such, expense accruals related to clinical trials and contract manufacturing are recognized based on the Company’s estimate of the degree of completion of the events specified in the specific clinical study or trial contract or drug development and manufacturing contract, respectively. The Company does not make significant estimates where costs incurred are supported by invoices or reports of costs incurred are obtained from a vendor that is directly performing the underlying services, such as a consultant or contract manufacturing organization. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the Consolidated Financial Statements as prepaid or accrued research and development. Amounts due may be fixed fee, fee for service, and may include upfront payments, monthly payments, and payments upon the completion of milestones or receipt of deliverables. Nonrefundable advance payments for goods and services that will be used or received in future research and development activities are deferred and recognized as expense in the period in which the related goods are delivered or services are performed. The Company has acquired and may continue to acquire the rights to develop and commercialize new drug candidates from third parties. The upfront payments to acquire license, product or rights, as well as any future milestone payments, are immediately recognized as research and development expense provided that the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use. Share-based Compensation The Company’s share-based compensation programs include options for the purchase of shares and restricted share units (RSUs). Such awards may be granted to employees, directors, and non-employee service providers. The Company measures compensation expense for all share-based awards at the grant date based on the fair value measurement of the award. Share-based compensation expense is recognized on a straight-line basis over the requisite service period, which is generally the vesting period, for each award. The fair value of RSUs is based on the closing market price of the Company’s ordinary shares on the date of grant. To determine the fair value of options for the purchase of shares, the Company uses the Black-Scholes option-pricing model. The determination of fair value using the Black-Scholes option-pricing model is affected by the Company’s share price as well as assumptions regarding a number of complex and subjective variables. Judgment is required in determining the assumptions used in these models which include the risk-free interest rate, expected term, expected volatility and expected dividend yield. The Company uses its historical volatility for the Company's shares to estimate expected volatility. The simplified method has been used to estimate the expected term of all options in previous years. Beginning January 1, 2023, expected term is estimated based on historical experience. Share-based compensation expense recognized in the Consolidated Statements of Operations is based on awards expected to vest and therefore the amount of expense has been reduced for estimated forfeitures which are based on historical experience. Share-based compensation expense is adjusted in subsequent periods for actual forfeitures. The Company records any excess tax benefits or tax shortfalls from its equity awards in its Consolidated Statements of Operations in the reporting periods in which options for the purchase of shares are exercised or RSUs vest. Income Taxes The Company files its own U.S. and foreign income tax returns and income taxes are presented in the Consolidated Financial Statements using the asset and liability method prescribed by the accounting guidance for income taxes. Deferred tax assets (“DTAs”) and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using the enacted tax rates projected to be in effect for the year in which the differences are expected to reverse. Net deferred tax assets are recorded to the extent the Company believes that these assets will more likely than not be realized. In making such determination, all available positive and negative evidence is considered, including scheduled reversals of deferred tax liabilities, recent cumulative earnings/losses by taxing jurisdiction, projected future taxable income, tax planning strategies and recent financial operations. Actual operating results in future years could differ from our current assumptions, judgments and estimates. The Company’s significant tax jurisdictions are Ireland and the United States. Estimates are required in determining the Company’s provision for income taxes. Some of these estimates are based on management’s interpretations of jurisdiction-specific tax laws or regulations. Various internal and external factors may have favorable or unfavorable effects on the future effective income tax rate of the business. These factors include, but are not limited to, changes in tax laws, regulations and/or rates, changing interpretations of existing tax laws or regulations, changes in estimates of prior years’ items, past and future levels of R&D spending, the impact of accounting for share-based compensation, and changes in overall levels of income before taxes. The Company did not recognize certain tax benefits from uncertain tax positions within the provision for income taxes. The tax benefit from an uncertain tax position is recognized only if it is more likely than not the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon settlement. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Interest and penalties related to unrecognized tax benefits are accounted for in income tax expense. Net Income (Loss) per Ordinary Share Basic net income (loss) per ordinary share is calculated by dividing net income (loss) by the weighted-average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed based on the treasury stock method by dividing net income by the weighted-average number of ordinary shares outstanding, plus potentially dilutive ordinary equivalent shares outstanding. However, where there is a net loss, no adjustment is made for potentially issuable ordinary shares because their effect would be anti-dilutive and therefore diluted net loss per share is equal to basic net loss per share. Comprehensive Loss Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). The Company has no components of other comprehensive income (loss). Therefore, net income (loss) equals comprehensive income (loss) for all periods presented and, accordingly, the Consolidated Statements of Comprehensive Income (Loss) is not presented in a separate statement. Segment and Concentration of Risks The Company operates in one segment. The Company’s chief operating decision maker (the “CODM”), its Chief Executive Officer, manages the Company’s operations and evaluates the Company’s financial performance on a consolidated basis for purposes of allocating resources. Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and accounts receivable. The Company places its cash equivalents with high credit quality financial institutions and, by policy, limits the amount of credit exposure with any one financial institution. Deposits held with banks have exceeded, and will continue to exceed, federally insured limits. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash and cash equivalents. The Company has not experienced any losses on its deposits of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's Consolidated Balance Sheet. The Company’s business is primarily conducted in U.S. dollars except for its agreements with contract manufacturers for drug supplies which are primarily denominated in Euros. The Company recorded a loss on foreign currency exchange rate differences of approximately $458,000, $397,000 and $96,000 during the years ended December 31, 2023, 2022 and 2021, respectively. If the Company increases its business activities that require the use of foreign currencies, it may be exposed to losses if the Euro and other such currencies continue to strengthen against the U.S. dollar. As of December 31, 2023, and 2022, $3.8 million and $1.7 million, respectively, of the Company’s property and equipment, net were held in the U.S. and a nominal amount were in Ireland. The Company does not own or operate facilities for the manufacture, packaging, labeling, storage, testing or distribution of nonclinical or clinical supplies of any of its drug candidates. The Company instead contracts with and relies on third-parties to manufacture, package, label, store, test and distribute all preclinical development and clinical supplies of our drug candidates, and it plans to continue to do so for the foreseeable future. The Company also relies on third-party consultants to assist in managing these third-parties and assist with its manufacturing strategy. Recent Accounting Pronouncements On November 27, 2023, the FASB issued Accounting Standards Update 2023-07 ("ASU 2023-07"), Segment Reporting- Improvements to Reportable Segment Disclosures, which requires public entities to provide disclosures on significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit or loss and other segment items on an annual and interim basis. The guidance also requires public entities to provide all disclosures about reportable segment’s profit or loss and assets in interim periods that are currently required annually. Public entities with a single reportable segment have to provide all disclosures required by Accounting Standards Codification (ASC) 280, Segment Reporting including the significant segment expense disclosures. The guidance is applied retrospectively to all periods presented in financial statements and is effective for fiscal years beginning after December 15, 2023, and for interim periods beginning after December 15, 2024. Early adoption is permitted. In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures, which requires public business entities to disclose a tabular reconciliation using both percentages and amounts, broken out into specific categories with certain reconciling items at or above 5% of the expected tax further broken out by nature and/or jurisdiction. The guidance also requires all entities to disclose income taxes paid, net of refunds, disaggregated by federal (national), state and foreign taxes for annual periods and to disaggregate the information by jurisdiction based on a quantitative threshold. All entities are required to apply the guidance prospectively, with the option to apply it retrospectively. The guidance is effective for the Company’s fiscal year beginning January 1, 2025. Early adoption is permitted.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures certain financial assets and liabilities at fair value on a recurring basis, including cash equivalents. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. A three-tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value: Level 1 — inputs are quoted prices (unadjusted) for identical assets or liabilities in active markets. Level 2 — inputs are other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 — inputs are unobservable inputs that are supported by little or no market activities, which would require the Company to develop its own assumptions. The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The carrying amounts reflected in the Consolidated Balance Sheets for cash equivalents, prepaid expenses and other current assets, accounts receivable, accounts payable and accrued liabilities, approximate their fair value due to their short-term nature. Based on the fair value hierarchy, the Company classifies its cash equivalents within Level 1. This is because the Company values its cash equivalents using quoted market prices. The Company’s Level 1 securities consisted of $589.9 million and $599.1 million in money market funds included in cash and cash equivalents at December 31, 2023, and 2022, respectively.

Composition of Certain Balance

Composition of Certain Balance Sheet Items	12 Months Ended
	Dec. 31, 2023
Composition of Certain Balance Sheet Items [Abstract]
Composition of Certain Balance Sheet Items	Composition of Certain Balance Sheet Items Prepaid Expenses and Other Current Assets Prepaid and other current assets consisted of the following (in thousands): December 31, 2023 2022 Prepaid R&D expenses $ 10,998 $ 5,325 Prepaid G&A expenses 803 1,597 Receivable from stock option exercises in-transit — 62 Other 2,140 1,708 Prepaid and other current assets $ 13,941 $ 8,692 Property and Equipment, net Property and equipment, net consisted of the following (in thousands): December 31, 2023 2022 Machinery and equipment $ 9,019 $ 9,901 Leasehold improvements — 1,498 Purchased computer software 2,232 1,500 11,251 12,899 Less: accumulated depreciation and amortization (7,415) (11,168) Property and equipment, net $ 3,836 $ 1,731 In December 2023, as a result of the expiration of the Company’s operating lease for its former South San Francisco facility (see Note 6, “Commitments and Contingencies”), the Company disposed of certain property and equipment with a total net book value of $15 thousand. The Company recognized a gain on disposal of $22 thousand for the year ended December 31, 2023. Depreciation expense was $0.9 million , $0.7 million, and $1.1 million for the years ended December 31, 2023, 2022 and 2021, respectively. Other Current Liabilities Other current liabilities consisted of the following (in thousands): December 31, 2023 2022 Payroll and related expenses $ 13,245 $ 11,060 Professional services 288 605 Other 2,129 503 Other current liabilities $ 15,662 $ 12,168

Net Income (Loss) Per Ordinary

Net Income (Loss) Per Ordinary Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Income (Loss) per Ordinary Share	Net Income (Loss) Per Ordinary Share Net income (loss) per ordinary share was determined as follows (in thousands, except per share amounts): Year Ended 2023 2022 2021 Numerator: Net income (loss) $ (147,028) $ (116,949) $ 66,975 Denominator: Weighted-average ordinary shares outstanding used in per share calculations - basic 53,216 47,369 44,228 Dilutive effect of shares issuable under equity incentive plans — — 4,236 Weighted-average ordinary shares outstanding used in per share calculations - diluted 53,216 47,369 48,464 Net income (loss) per share: Basic net income (loss) per ordinary share $ (2.76) $ (2.47) $ 1.51 Diluted net income (loss) per ordinary share $ (2.76) $ (2.47) $ 1.38 Potentially issuable ordinary shares were not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive due to the loss recorded during the years ended December 31, 2023 and 2022, and therefore diluted net loss per share is equal to basic net loss per share. During the year ended December 31, 2021, diluted net income p er ordinary share is computed by dividing net income by the weighted average ordinary shares outstanding during the period plus potentially dilutive ordinary equivalent shares outstanding. The equivalent ordinary shares not included in diluted net income (loss) per share because their effect would be anti-dilutive are as follows (in thousands): Year Ended 2023 2022 2021 Stock options to purchase ordinary shares 9,866 9,480 382 Restricted Stock Units (RSU) 25 23 — Total 9,891 9,503 382

Commitment and Contingencies

Commitment and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitment and Contingencies	Commitments and Contingencies Lease Commitments As of December 31, 2023, the Company currently has three leases relating to its facilities in Brisbane, California, and Dublin, Ireland. South San Francisco Facility The Company had a noncancelable operating sublease (the “SSF Lease”) covering 128,751 square feet of office and laboratory space in South San Francisco, California, U.S. (the “SSF Facility”), which expired on December 31, 2023. Total operating lease cost was $6.3 million , $6.3 million and $6.3 million for the years ended December 31, 2023, 2022 and 2021, respectively. Total cash paid against the operating lease liability was $6.5 million , $6.3 million and $6.2 million for the years ended December 31, 2023, 2022 and 2021 respectively. The Company obtained a standby letter of credit which could be drawn down by the sublandlord in the event the Company fails to fully and faithfully perform all of its obligations under the SSF Lease and to compensate the sublandlord for all losses and damages the sublandlord may suffer as a result of the occurrence of any default on the part of Company not cured within the applicable cure period. This standby letter of credit is collateralized by a certificate of deposit of the same amount which is classified as restricted cash. As of December 31, 2023, none of the remaining standby letter of credit amount of $1.4 million included in restricted cash, current has been used and the Company expects that the outstanding balance will be returned by April 2024. Sub-Sublease of South San Francisco Facility The Company had a Sub-Sublease Agreement (the “Sub-Sublease”) with Assembly Biosciences, Inc. covering approximately 46,641 square feet of office and laboratory space of the SSF Facility. The Sub-Sublease expired on December 15, 2023, in connection with the expiration of the Lease. The Sub-Sublease was considered an operating lease under ASC 842. For the years ended December 31, 2023, 2022 and 2021, the Company recorded $2.8 million , $2.9 million and $2.9 million respectively, of sub-lease rental income as an offset to its operating expenses. Dublin In June 2021, the Company entered into a lease agreement for office space in Dublin, Ireland, which commenced in August 2021 and had an initial term of one year. In April 2023, the Company renewed the lease for another one year term with a termination date of July 2024. In addition, the Company entered into a lease agreement for additional office space in Dublin, Ireland, which commenced in August 2023 and has an initial term of one year. Both of these leases have an automatic renewal clause, pursuant to which the agreement will be extended automatically for successive periods equal to the current term, unless the agreement is cancelled by the Company. Brisbane Facility On October 28, 2022, the Company, entered into a noncancelable operating sublease (the "Brisbane Sublease") to sublease approximately 31,157 square feet of office and laboratory space located in Brisbane, California (the “Brisbane Facility”) with Arcus Biosciences, Inc., (the "Sublandlord"). The Brisbane Sublease became effective on Octobe r 28, 2022. The Brisbane Sublease provides that the Company's obligation to pay rent commenced on July 1, 2023, which is subject to abatement for the first six months following such date, with the exception of the seventh rent payment that was due upon execution of the Brisbane Sublease. The Company is obligated to make lease payments totaling approximately $14.9 million over the lease term, which expires on September 30, 2028, unless terminated earlier. The Brisbane Sublease further provides that the Company is obligated to pay to the Sublandlord certain costs, including taxes and operating expenses. The Company has the option to extend the sublease by providing written notice at least nine months prior to the expiration of the sublease term. As of December 31, 2023, the Brisbane Sublease has a remaining lease term of 4.75 years. The Brisbane Sublease is considered an operating lease and the accounting lease commencement date was on July 31, 2023 when the Company gained control over of the Brisbane Facility. The Company recorded a right-of-use asset of approximately $11.4 million and lease liability of approximately $3.6 million relating to the Brisbane Sublease on the lease commencement date. The discount rate used to determine the lease liability was 5.76%. The initial measurement of the right-of-use asset for the Brisbane Sublease includes the tenant improvement added by the Company wherein the lessor was deemed the accounting owner. The Company is entitled to an improvement allowance of up to $9.3 million , to be used for costs incurred by the Company to construct certain improvements to the Brisbane Facility and to prepare for the Company's occupancy of the Brisbane Facility. As of December 31, 2023, $8.2 million has been received from the Sublandlord and the Company is obligated to fund construction costs incurred in excess of the improvement allowance. Total o perating lease cost for the Brisbane Sublease was $1.3 million for the year ended December 31, 2023 . Total cash paid against the operating lease liability was $0.4 million for the year ended December 31, 2023 . In conjunction with the Brisbane Sublease, the Company obtained a standby letter of credit in the initial amount of $0.9 million, which may be drawn down by the Sublandlord in the event the Company fails to fully and faithfully perform all of its obligations under the Brisbane Sublease and to compensate the Sublandlord for all losses and damages the Sublandlord may suffer as a result of the occurrence of any default on the part of the Company not cured within the applicable cure period. As of December 31, 2023, none of the standby letter of credit amount of $0.9 million has been used. Future minimum payments under the above-described noncancelable operating leases, including a reconciliation to the lease liabilities recognized in the Consolidated Balance Sheets as of December 31, 2023, are as follows (in thousands): Year Ended December 31, Operating Leases 2024 2,833 2025 3,052 2026 3,158 2027 3,269 2028 2,523 Thereafter — Total $ 14,835 Less: Present value adjustment (3,000) Lease liability $ 11,835 Indemnity Obligations The Company has entered into indemnification agreements with its current and former directors and officers and certain key employees. These agreements contain provisions that may require the Company, among other things, to indemnify such persons against certain liabilities that may arise because of their status or service and advance their expenses incurred as a result of any indemnifiable proceedings brought against them. The obligations of the Company pursuant to the indemnification agreements continue during such time as the indemnified person serves the Company and continues thereafter until such time as a claim can be brought. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has a director and officer liability insurance policy that limits its exposure and enables the Company to recover a portion of any future amounts paid. As a result of its insurance policy coverage, the Company believes the estimated fair value of these indemnification agreements is minimal. Accordingly, the Company had no liabilities recorded for these agreements as of December 31, 2023, and 2022. Other Commitments In the normal course of business, the Company enters into various firm purchase commitments primarily related to research and development activities. As of December 31, 2023, the Company had non-cancelable purchase commitments to suppliers for $12.4 million of which $6.3 million is included in current liabilities, and contractual obligations under license agreements of $0.4 million of which $60,000 is included in current liabilities. The following is a summary of the Company's non-cancelable purchase commitments and contractual obligations as of December 31, 2023 (in thousands): Total 2024 2025 2026 2027 2028 Thereafter Purchase Obligations (1) $ 12,433 $ 12,397 $ 36 $ — $ — $ — $ — Contractual obligations under license agreements 398 124 64 60 60 45 45 Total $ 12,831 $ 12,521 $ 100 $ 60 $ 60 $ 45 $ 45 ________________ (1) Purchase obligations consist of non-cancelable purchase commitments to suppliers and contract research organizations. Legal Proceedings We are not currently a party to any material legal proceedings. We may at times be party to ordinary routine litigation incidental to our business. When appropriate in management's estimation, we may record reserves in our financial statements for pending legal proceedings.

Significant Agreements

Significant Agreements	12 Months Ended
	Dec. 31, 2023
Collaborative Agreement [Abstract]
Significant Agreements	Significant Agreements Roche License Agreement In December 2013, the Company through its wholly owned subsidiary Prothena Biosciences Limited and Prothena Biosciences Inc entered into a License, Development, and Commercialization Agreement (the “License Agreement”) with F. Hoffmann-La Roche Ltd. and Hoffmann-La Roche Inc. (together, “Roche”) to develop and commercialize certain antibodies that target α - synuclein, including prasinezumab, which are referred to collectively as “Licensed Products.” Upon the effectiveness of the License Agreement in January 2014, the Company granted to Roche an exclusive, worldwide license to develop, make, have made, use, sell, offer to sell, import and export the Licensed Products. The Company retained certain rights to conduct development of the Licensed Products and a n option to co-promote prasinezumab in the U.S. During the term of the License Agreement, the Company and Roche will work exclusively with each other to research and develop antibody products targeting alpha-synuclein (or α - synuclein) potentially including incorporation of Roche’s proprietary Brain Shuttle™ technology to potentially increase delivery of therapeutic antibodies to the brain. The License Agreement provided for Roche making an upfront payment to the Company of $30.0 million, which was received in February 2014; making a clinical milestone payment of $15.0 million upon initiation of the Phase 1 clinical trial for prasinezumab, which was received in May 2014; making a clinical milestone payment of $30.0 million upon dosing of the first patient in the Phase 2 clinical trial for prasinezumab, which was achieved in June 2017; and making a clinical milestone payment of $60.0 million upon dosing of the first patient in the global Phase 2b PADOVA study for prasinezumab, which was achieved in May 2021. For prasinezumab, Roche is obligated to pay: • up to $290.0 million upon the achievement of development, regulatory, and various first commercial sales milestones; • up to $155.0 million upon achievement of U.S. commercial sales milestones; • up to $175.0 million upon achievement of ex-U.S. commercial sales milestones; and • tiered, high single-digit to high double-digit royalties in the teens based on U.S. and ex-U.S. annual net sales, subject to certain adjustments, with respect to the applicable Licensed Product. Roche bore 100% of the cost of conducting the research collaboration under the License Agreement during the research term, which expired December 31, 2017. In May 2021, the Company exercised its rights under the terms of License Agreement to receive potential U.S. commercial sales milestone and royalties, in lieu of a U.S. profit and loss share for prasinezumab in Parkinson’s disease. Thus in the U.S., through May 28, 2021, the parties shared all development costs, all of which were allocated 70% to Roche and 30% to the Company, for prasinezumab in the Parkinson’s disease indication. If the Company opts in to participate in co-development and co-funding for any other Licensed Products and/or indications, the parties will share all development and commercialization costs, as well as profits, all of which will be allocated 70% to Roche and 30% to the Company. The Company initiated a Phase 1 clinical trial for prasinezumab in 2014. Following the Phase 1 clinical trial, Roche became primarily responsible for developing, obtaining and maintaining regulatory approval for and commercializing Licensed Products. Roche also became responsible for the clinical and commercial manufacture and supply of Licensed Products. In addition, the Company has an option under the License Agreement to co-promote prasinezumab in the U.S. in the Parkinson’s disease indication. If the Company exercises such option, it may also elect to co-promote additional Licensed Products in the U.S. approved for Parkinson’s disease. Outside the U.S., Roche will have responsibility for developing and commercializing the Licensed Products. Roche bears all costs that are specifically related to obtaining or maintaining regulatory approval outside the U.S. and will pay the Company a variable royalty based on annual net sales of the Licensed Products outside the U.S. The License Agreement continues on a country-by-country basis until the expiration of all payment obligations under the License Agreement. The License Agreement may also be terminated (i) by Roche at will after the first anniversary of the effective date of the License Agreement, either in its entirety or on a Licensed Product-by-Licensed Product basis, upon 90 days’ prior written notice to the Company prior to first commercial sale and 180 days’ prior written notice to Prothena after first commercial sale, (ii) by either party, either in its entirety or on a Licensed Product-by-Licensed Product or region-by-region basis, upon written notice in connection with a material breach uncured 90 days after initial written notice, and (iii) by either party, in its entirety, upon insolvency of the other party. The License Agreement may be terminated by either party on a patent-by-patent and country-by-country basis if the other party challenges a given patent in a given country. The Company’s rights to co-develop Licensed Products under the License Agreement will terminate if the Company commences certain studies for certain types of competitive products. The Company’s rights to co-promote Licensed P roducts under the License Agreement will terminate if the Company commences a Phase 3 study for such competitive products. The License Agreement cannot be assigned by either party without the prior written consent of the other party, except to an affiliate of such party or in the event of a merger or acquisition of such party, subject to certain conditions. The License Agreement also includes customary provisions regarding, among other things, confidentiality, intellectual property ownership, patent prosecution, enforcement and defense, representations and warranties, indemnification, insurance, and arbitration and dispute resolution. Performance Obligations As of December 31, 2023, and December 31, 2022, there were no re maining performance obligations under License Agreement since the obligations related to research and development activities were only for the Phase 1 clinical trial and the remaining obligations were delivered or performed. Revenue and Expense Recognition No collaboration revenue from Roche was recognized for the years ended December 31, 2023, and 2022, respectively as compared to $60.2 million for the year ended December 31, 2021. For the year ended December 31, 2021 collaboration revenue from Roche included a $60.0 million clinical milestone recognized upon first patient dosed in the PADOVA study. Through May 28, 2021, cost sharing payments to Roche were recorded as R&D expenses. The Company recognized nil in R&D expenses for payments made to Roche during the years ended December 31, 2023, and 2022, respectively, as compared to $7.2 million for the year ended December 31, 2021 . The Company had accounts receivable from Roche of nil at December 31, 2023, and 2022, respectively. Milestone Accounting Under the License Agreement, the Company is eligible to receive certain milestone payments upon the achievement of development, regulatory and various first commercial sales milestones. Milestone payments are evaluated under ASC Topic 606. Factors considered in this determination included scientific and regulatory risk that must be overcome to achieve each milestone, the level of effort and investment required to achieve the milestone, and the monetary value attributed to the milestone. Accordingly, the Company estimates payments in the transaction price based on the most likely approach, which considers the single most likely amount in a range of possible amounts related to the achievement of these milestones. Additionally, milestone payments are included in the transaction price only when the Company can conclude it is probable that a significant revenue reversal will not occur in future periods when the milestone is achieved. The Company excludes the milestone payments and royalties in the initial transaction price calculation because such payments are considered to be variable considerations with constraint. Such milestone payments and royalties will be recognized as revenue once the Company can conclude it is probable that a significant revenue reversal will not occur in future periods. The clinical and regulatory milestones under the License Agreement after the point at which the Company could opt out are considered to be variable considerations with constraint due to the fact that active participation in the development activities that generate the milestones is not required under the License Agreement, and the Company can opt out of these activities. There are no refunds or claw-back provisions and the milestones are uncertain of occurrence even after the Company has opted out. Based on this determination, these milestones will be recognized when the Company can conclude it is probable that a significant revenue reversal will not occur in future periods. Collaboration Agreement with Bristol Myers Squibb Overview On March 20, 2018, the Company, through its wholly owned subsidiary Prothena Biosciences Limited (“PBL”), entered into a Master Collaboration Agreement (the “Collaboration Agreement”) with Celgene Switzerland LLC (“Celgene”), a subsidiary of Celgene Corporation (which was acquired by Bristol Myers Squibb (“BMS”) in November 2019), pursuant to which Prothena granted to Celgene a right to elect in its sole discretion to exclusively license rights both in the U.S. (the “US Rights”) and on a global basis (the “Global Rights”), with respect to the Company’s programs to develop and commercialize antibodies targeting tau, TDP-43 and an undisclosed target (the “Collaboration Targets”). For each such program, BMS may exercise its US Rights at the IND filing, and if it so exercises such US Rights would also have a right to expand the license to Global Rights. If BMS exercises its US Rights for a program, then following the first to occur of (a) completion by the Company, in its discretion and at its cost, of Phase 1 clinical trials for such program or (b) the date on which BMS elects to assume responsibility for completing such Phase 1 clinical trials (at its cost), BMS would have decision making authority over development activities and all regulatory, manufacturing and commercialization activities in the U.S. As discussed below, BMS exercised its US Rights for the tau/BMS-986446 (formerly PRX005) Collaboration Target and on July 30, 2021, PBL entered into a U.S. License Agreement granting BMS the exclusive license to develop, manufacture and commercialize antibody products in the United States targeting tau (the “Tau US License Agreement”). Subsequently, BMS exercised its Global Rights for the tau/BMS-986446 Collaboration Target and on July 5, 2023, PBL entered into a Global License Agreement granting BMS the exclusive license to develop, manufacture and commercialize tau Collaboration Products globally for any and all uses or purposes with respect to any human or animal disease, disorder or condition (the “Tau Global License Agreement”). The Tau Global License Agreement supersedes and replaces the Tau US License Agreement in its entirety. The Collaboration Agreement provided for Celgene making an upfront payment to the Company of $100.0 million which was received in April 2018, plus future potential license exercise payments and regulatory and commercial milestones for each program under the Collaboration Agreement, as well as royalties on net sales of any resulting marketed products. In connection with the Collaboration Agreement, the Company and Celgene entered into a Share Subscription Agreement on March 20, 2018, under which Celgene subscribed to 1,174,536 of the Company’s ordinary shares for a price of $42.57 per share, for a total of approximately $50.0 million. BMS US and Global Rights and Licenses On a program-by-program basis, beginning on the effective date of the Collaboration Agreement and ending on the date that the IND Option term expires for such program (which generally occurs sixty days after the date on which the Company delivers to BMS the first complete data package for an IND that was filed for a lead candidate from the relevant program), BMS may elect in its sole discretion to exercise its US Rights to receive an exclusive license to develop, manufacture and commercialize antibodies targeting the applicable Collaboration Target in the U.S. (the “US License”). If BMS exercises its US Rights for a collaboration program, it is obligated to pay the Company an exercise fee of approximately $80.0 million per program. Thereafter, following the first to occur of (a) completion by the Company, in its discretion and at its cost, of Phase 1 clinical trials for such program or (b) BMS’ election to assume responsibility to complete such Phase 1 clinical trials (at its cost), BMS would have the sole right to develop, manufacture and commercialize antibody products targeting the relevant Collaboration Target for such program (the “Collaboration Products”) in the U.S. On a program-by-program basis, following completion of a Phase 1 clinical trial for a collaboration program for which BMS has previously exercised its US Rights, BMS may elect in its sole discretion to exercise its Global Rights with respect to such collaboration program to receive a worldwide, exclusive license to develop, manufacture and commercialize antibodies targeting the applicable Collaboration Target (the “Global License”). If BMS exercises its Global Rights, BMS would be obligated to pay the Company an additional exercise fee of $55.0 million for such collaboration program. The Global Rights would then replace the US Rights for that collaboration program, and BMS would have decision making authority over developing, obtaining and maintaining regulatory approval for, manufacturing and commercializing the Collaboration Products worldwide. After BMS’ exercise of Global Rights for a collaboration program, the Company is eligible to receive up to $562.5 million in regulatory and commercial milestones per program. Following an exercise by BMS of either US Rights or Global Rights for such collaboration program, the Company will also be eligible to receive tiered royalties on net sales of Collaboration Products ranging from high single digit to high teen percentages, on a weighted average basis depending on the achievement of certain net sales thresholds. Such exercise fees, milestones and royalty payments are subject to certain reductions as specified in the Collaboration Agreement, the agreement for US Rights and the agreement for Global Rights. BMS will continue to pay royalties on a Collaboration Product-by-Collaboration Product and country-by-country basis, until the latest of (i) expiration of certain patents covering the Collaboration Product, (ii) expiration of all regulatory exclusivity for the Collaboration Product, and (iii) an agreed period of time after the first commercial sale of the Collaboration Product in the applicable country (the “Royalty Term”). Term and Termination The research term under the Collaboration Agreement continues for a period of six years, which BMS may extend for up to two additional 12-month periods by paying an extension fee of $10.0 million per extension period. The term of the Collaboration Agreement continues until the last to occur of the following: (i) expiration of the research term; (ii) expiration of all US Rights terms; and (iii) expiration of all Global Rights terms. The term of any US License or Global License would continue on a Licensed Product-by-Licensed Product and country-by-country basis until the expiration of all Royalty Terms under such agreement. The Collaboration Agreement may be terminated (i) by either party on a program-by-program basis if the other party remains in material breach of the Collaboration Agreement following a cure period to remedy the material breach, (ii) by BMS at will on a program-by-program basis or in its entirety, (iii) by either party, in its entirety, upon insolvency of the other party, or (iv) by the Company, in its entirety, if BMS challenges a patent licensed by the Company to BMS under the Collaboration Agreement. Performance Obligations The Company assessed the Collaboration Agreement and concluded that it represented a contract with a customer within the scope of ASC 606. Per ASC 606, a performance obligation is defined as a promise to transfer a good or service or a series of distinct goods or services. At inception of the Collaboration Agreement, the Company is not obligated to transfer US Licenses or Global Licenses to BMS unless BMS exercises its US Rights or Global Rights, respectively, and the Company is not obligated to perform development activities under the development plan during preclinical and Phase 1 clinical trials including the regulatory filing of the IND. The discovery, preclinical and clinical development activities performed by the Company are to be performed at the Company’s discretion and are not promised goods or services and therefore are not considered performance obligations under ASC 606, unless and until the Company agrees to perform the Phase 1 clinical trials (after the IND option exercise) that are determined to be performance obligations at the time the option is exercised. Per the terms of the Collaboration Agreement, the Company may conduct discovery activities to characterize, identify and generate antibodies to become collaboration candidates that target such Collaboration Target, and thereafter may pre-clinically develop collaboration candidates to identify lead candidates that target such Collaboration Target and file an IND with the U.S. Food and Drug Administration (the “FDA”) for a Phase 1 clinical trial for such lead candidates. In the event the Company agrees to be involved in a Phase 1 clinical trial, the Company will further evaluate whether any such promise represents a performance obligation at the time the option is exercised. If it is concluded that the Company has obligated itself to an additional performance obligation besides the license granted at IND option exercise, then the effects of the changes in the arrangement will be evaluated under the modification guidance of ASC 606. The Company is not obligated to perform manufacturing activities. Per the terms of the Collaboration Agreement, to the extent that the Company, at its discretion, conducts a program, the Company shall be responsible for the manufacture of collaboration candidates and collaboration products for use in such program, as well as the associated costs. Delivery of manufactured compound (clinical product supply) is not deemed a performance obligation under ASC 606 as the Company is not obligated to transfer supply of collaboration product to BMS unless BMS exercises its right to participate in the Phase 1 development. Compensation for the Company’s provision of inventory supply, to the extent requested by BMS would be paid to the Company by BMS at a reasonable stand-alone selling price for such supply. Given that (i) there is substantial uncertainty about the development of the programs, (ii) the pricing for the inventory is at its standalone selling price and (iii) the manufacturing services require the entity to transfer additional goods or services that are incremental to the goods and services provided prior to the resolution of the contingency, the Company’s supply of product is not a material right. Therefore, the inventory supply is not considered a performance obligation unless and until, requested by BMS. In addition to the grant of the US License after BMS exercises its US Rights for a program, BMS is entitled to receive certain ancillary development services from the Company, such as technology transfer assistance, regulatory support, safety data reporting activities and transition supply, if requested by BMS. In addition to the grant of the Global License after BMS exercises the Global Rights for a program, BMS is entitled to receive certain ancillary development services from the Company, such as ongoing clinical trial support upon request by BMS, transition supply, if requested by BMS, and regulatory support for coordination of pharmacovigilance matters. The Company evaluated the potential obligations to transfer the US Licenses and Global Licenses and performance of the ancillary development services subsequent to exercise of the US Rights and Global Rights, if the options are exercised by BMS, under ASC 606-10-55-42 and 55-43 to determine whether the US Rights or the Global Rights provided BMS a “material right” and concluded that BMS’ options to exercise its US Rights and Global Rights represented “material rights” to BMS that it would not have received without entering into the Agreement. There were a total of six options at inception including US Rights and Global Rights to acquire a US License and a Global License, respectively, and rights to request certain development services (following exercise of the US Rights and Global Rights, respectively) for each of the three programs, with four options remaining as of December 31, 2023. The deferred revenue balance as of December 31, 2023 of $67.4 million related to the outstanding US Rights and Global Rights . Per ASC 606, the US Rights and Global Rights are material rights and therefore are performance obligations. The goods and services underlying the options are not accounted for as separate performance obligations, but rather become performance obligations, if and when, an option is exercised. US License Agreement for the Tau/BMS-986446 Collaboration Target On July 30, 2021, the Company entered into the Tau US License Agreement. The Tau US License Agreement included an upfront payment of $80.0 million. The Tau US License Agreement included the following distinct performance obligations: (1) the delivery of the US License for tau/BMS-986446 Collaboration Target (“Tau US License Obligation”); and (2) the Company’s obligation to provide development activities under the development plan during any Phase 1 clinical trials (the “Tau US Development Services Obligation”). Revenue allocated to the Tau US License Obligation is recognized when the Company has satisfied its obligation at a point in time, while the revenue allocated to the Tau US Development Services Obligation are recognized over time using an input-based model. Global License Agreement for the Tau/BMS-986446 Collaboration Target On July 5, 2023, the Company entered into the Tau Global License Agreement, which as discussed above supersedes and replaces the Tau US License Agreement in its entirety. The Company received the associated option exercise fee of $55.0 million in August 2023 and it will be eligible to receive regulatory and sales milestones up to $562.5 million upon achievement of certain developmental events, including regulatory approval of a tau Collaboration Product, and on BMS achieving certain annual net sales thresholds in the United States and worldwide. The Company also will be eligible to receive tiered royalties on net sales of tau Collaboration Products, ranging from high single digit to high teen percentages, on a weighted average basis depending on the achievement of certain net sales thresholds. The Company’s distinct performance obligation under the Tau Global License Agreement was limited to the delivery of the Global License for tau/ BMS-986446 Collaboration Target (“Tau Global License Obligation”). Revenue allocated to the Tau Global License Obligation is recognized when the Company has satisfied its obligation at a point in time. Transaction Price At the inception of the Collaboration Agreement, the Company did not transfer any goods or services to BMS that are material. Accordingly, the Company has concluded that the initial transaction price will be recognized as a contract liability and will be deferred until the Company transfers control of goods or services to BMS (which would be when BMS exercises the US Right or Global Right and receives control of the US License or Global License for at least one of the programs), or when the IND Option term expires if BMS does not exercise the US Right (which is generally sixty days after the date on which the Company delivers to BMS the first complete data package for an IND that was filed for a lead candidate from the relevant program), or when the Phase 1 Option term expires if BMS does not exercise the Global Right (which is generally ninety days after the date on which the Company delivers to BMS the first complete data package for a Phase 1 clinical trial for a lead candidate from the relevant program) or at the termination of the Collaboration Agreement, whichever occurs first. At such point that the Company transfers control of goods or services to BMS, or when the option expires, the Company will recognize revenue as a continuation of the original contract. Under this approach, the Company will treat the consideration allocated to the material right as an addition to the consideration for the goods or services underlying the contract option. At inception of the Collaboration Agreement, the Company estimated the standalone selling price for each performance obligation (i.e., the US Rights and Global Rights by program). The estimate of standalone selling price for the US Rights and Global Rights by program was based on the adjusted market assessment approach using a discounted cash flow model. The key assumptions used in the discounted cash flow model included the market opportunity for commercialization of each program in the U.S. or globally depending on the license, the probability of successfully developing and commercializing a given program target, the estimated remaining development costs for the respective program, the estimated time to commercialization of the drug for that program and a discount rate. The initial transaction price under the Collaboration Agreement, pursuant to ASC 606, was $110.2 million, including the $100.0 million upfront payment and $10.2 million premium on the ordinary shares purchased under the SSA. The Company allocated the initial transaction price across the US Rights and Global Rights for each program in a range of approximately $15-$25 million and $10-$18 million, respectively. The Company did not include the option fees in the initial transaction price because such fees are contingent on the options to the US Rights and the Global Rights being exercised. Upon the exercise of the US Rights and the Global Rights for a program, the Company will have the obligation to deliver the US License and Global License and provide certain ancillary developme nt services if requested by BMS, subsequent to its exercise of the US Rights and Global Rights, respectively, for such program. The Company will include the option fees in the transaction price at the point in time a material right is exercised and the Company transfers control of the goods and services to BMS. In ad dition, the Company did not include in the initial transaction price certain clinical and regulatory milestone payments since they relate to licenses for which BMS has not yet exercised its option to obtain and these variable considerations are constrained due to the likelihood of a significant revenue reversal. Upon entering into the Tau US License Agreement, the Company granted BMS a US License for the tau/BMS-986446 Collaboration Target, which transferred control of such underlying US License to BMS. Following execution of the Tau US License Agreement, BMS paid the Company a $80.0 million option exercise fee. Under the continuation of the original contract method, the Company computed the relative sales price after the Company transferred control of the US License for tau/BMS-986446. The Company used the original allocated consideration for the US Right for tau/BMS-986446 of $24.9 million (computed at the inception of the contract) plus the $80.0 million option exercise fee to arrive at the total transaction price of approximately $104.9 million. This total transaction price was further allocated using the relative sales price method between the Tau US License Obligation and the Tau US Development Services Obligation. The best estimate of selling price for the US License for tau/BMS-986446 was based on a discounted cash flow model. The key assumptions used in the discounted cash flow model used to determine the best estimate of selling price for the license included the market opportunity for commercialization of tau/BMS-986446, the probability of successfully developing/commercializing BMS-986446, the remaining development costs for tau/BMS-986446, and the estimated time to commercialization of tau/BMS-986446. Based on the relative selling price method, the amount that the Company allocated to the performance obligations is as follow s: $77.5 million to the license to be recognized concurrent with the delivery of the license; and $27.5 million as development services to be recognized based on percentage of completion over the service period. Upon entering into the Tau Global License Agreement, the Company granted BMS a Global License for the tau/BMS-986446 Collaboration Target, which transferred control of such underlying Global License to BMS. Following execution of the Tau Global License Agreement, BMS paid the Company a $55.0 million option exercise fee. Under the continuation of the original contract method, the Company computed the relative sales price after the Company transferred control of the Global License for tau/BMS-986446. The Company used the original allocated consideration for the Global Right for tau/BMS-986446 of $17.9 million (computed at the inception of the contract) plus the $55.0 million option exercise fee to arrive at the total transaction price of approximately $72.9 million. Given that the Company’s distinct performance obligation under the Tau Global License Agreement was limited to the Tau Global License Obligation no further allocation was required. Significant Payment Terms The upfront payment of $100.0 million was received in April 2018, while all option fees and milestone payments are due within 30 days after the achievement of the relevant milestone by BMS or receipt by BMS of an invoice for such an amount from the Company. The Collaboration Agreement does not have a significant financing component since a substantial amount of consideration promised by BMS to the Company is variable and the amount of such variable consideration varies based upon the occurrence or non-occurrence of future events that are not within the control of either BMS or the Company. Variable considerations related to clinical and regulatory milestone payments and option fees are constrained due to the likelihood of a significant revenue reversal. Revenue and Expense Recognition For the year ended December 31, 2023 , collaboration revenue from BMS was $91.3 million. Collaboration revenue for the year ended December 31, 2023 included $72.9 million recognized for the tau Global License Obligation ( $55.0 million tau global option exercise fee and $17.9 million of deferred revenue recognized for the Global Right for the tau Collaboration Product), $4.7 million under a supply agreement with BMS and the remainder was primarily recognized for tau US Development Services Obligation . For the year ended December 31, 2022, collaboration revenue from BMS recognized based on an input-based model included $13.9 million for tau US Development Services Obligation recognized as collaboration revenue. For the year ended December 31, 2021, collaboration revenue included $77.5 million in tau US License revenue and $2.2 million for tau US Development Service s Obligation for a total of $79.7 million in collaboration revenue. As of December 31, 2023 , the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied was nil. The Company had $5.2 million and nil accounts receivable from BMS at December 31, 2023 , and 2022, respectively. Deferred Revenue The deferred revenue balance at the beginning of the fiscal year was $96.7 million of which $17.9 million was recognized as revenue for the Global Right for the tau Collaboration Product and $11.4 million was recognized as revenue related to the Tau US Development Services Obligation performed during the fiscal year. As of December 31, 2023, the deferred revenue balance related to outstanding US Rights and Global Rights was $67.4 mil

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Shareholders' Equity	Shareholders' Equity Ordinary Shares As of December 31, 2023, the Company had 100,000,000 ordinary shares authorized for issuance with a par value of $0.01 per ordinary share an d 53,682,117 or dinary shares issued and outstanding. Each ordinary share is entitled to one vote and, on a pro rata basis, to dividends when declared and the remaining assets of the Company in the event of a winding up. As of December 31, 2023, 13,477,039 ordinary shares are reserved for issuance pursuant to outstanding and future equity awards under the Company’s equity incentive plans. Euro Deferred Shares As of December 31, 2023, the Company had 10,000 Euro Deferred Shares authorized for issuance with a nominal value of €22 per share. No Euro Deferred Shares are outstanding at December 31, 2023. The rights and restrictions attaching to the Euro Deferred Shares rank pari passu with the ordinary shares and are treated as a single class in all respects. March 2021 Offering In March 2021, the Company completed an underwritten public offering of an aggregate of 4,025,000 of its ordinary shares at a public offering price of $20.75 per ordinary share. The Company received aggregate net proceeds of approximately $78.0 million, after deducting the underwriting discount and offering costs. December 2022 Offering In December 2022, the Company completed an underwritten public offering of an aggregate of 3,250,000 of its ordinary shares at a public offering price of $56.50 per ordinary share. The Company received aggregate net proceeds of approximately $172.4 million, after deducting the underwriting discount and offering costs. In January 2023, the Company issued an additional 395,096 ordinary shares resulting from the underwriters’ partial exercise of their 30-day option to purchase up to an additional 487,500 ordinary shares of as part of the December 2022 underwritten public offering. The Company received approximately $20.9 million proceeds from the exercise, net of underwriting discount but before deducting any offering costs. At-the-Market Offerings In May 2021, the Company entered into an Equity Distribution Agreement (the “May 2021 Distribution Agreement”), pursuant to which the Company could issue and sell, from time to time, shares of the Company's ordinary shares. In connection with entering into the May 2021 Distribution Agreement, on May 28, 2021, the Company filed with the SEC a prospectus supplement relating to the offer, issuance and sale of up to $100.0 million of the Company’s ordinary shares pursuant to the May 2021 Distribution Agreement. For the year ended December 31, 2021, t he Company issued 1,640,174 ordinary shares pursuant to the May 2021 Distribution Agreement, for total gross proceeds of approximately $100.0 million before deducting underwriting discounts, commissions, and other offering expenses payable by the Company of $3.2 million. The May 2021 Distribution Agreement was no longer effective as of December 23, 2021. In December 2021, the Company entered into an Equity Distribution Agreement (the “December 2021 Distribution Agreement”), pursuant to which the Company may issue and sell, from time to time, the Company's ordinary shares. In connection with entering into the December 2021 Distribution Agreement, on December 23, 2021, the Company filed with the SEC a prospectus supplement relating to the offer, issuance and sale of up to $250.0 million of the Company’s ordinary shares pursuant to the December 2021 Distribution Agreement. For the years ended December 31, 2023, and 2022, respectively, t he Company sold and issued 42,361 and 911,228 ordinary shares, pursuant to the December 2021 Distribution Agreement, for total gross proceeds of approximately $3.2 million and $53.1 million before deducting underwriting discounts, commissions, and other offering expenses payable by the Company of $0.1 million and $1.7 million .

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation	Share-Based Compensation Equity Incentive Plans The Company’s equity incentive plans, the 2018 Long Term Incentive Plan, as amended (the “2018 LTIP”), 2020 Employment Inducement Incentive Plan, as amended (the “2020 EIIP”), and previously, the Amended and Restated 2012 Long Term Incentive Plan (the “2012 LTIP”), reserve ordinary shares for the issuance of stock options , stock appreciation rights, restricted shares, RSUs, performance bonus awards, performance share units awards, dividend equivalents and other share or cash-based awards to eligible individuals. Options granted under each of the 2018 LTIP, 2020 EIIP, and 2012 LTIP expire no later than ten years from the date of grant. In May 2023, the Company’s shareholders approved an amendment to the 2018 LTIP to increase the number of ordinary shares available for issuance under the 2018 LTIP by 2,000,000 ordinary shares. As of December 31, 2023, the number of ordinary shares authorized under the 2018 LTIP was 14,614,183. Upon adoption of the 2018 LTIP, no new awards are permitted under the 2012 LTIP. As of December 31, 2023 , the number of ordinary shares authorized under the 2020 EIIP was 1,485,000 and 58,750 ordinary shares remained available for future awards under the 2020 EIIP. The Company’s Board of Directors has adopted a series of amendments to increase the ordinary shares available for issuance under the 2020 EIIP and it reserves the right to both amend the 2020 EIIP to increase the number of ordinary shares available and make additional awards to key new hires. The Company’s option awards generally vest over four years, while RSUs vest over two years. As of December 31, 2023 , 3,585,452 ordinary shares remained available for grant under its equity plans . Share-based Compensation Expense Share-based compensation expense recorded in these Consolidated Financial Statements for the years ended December 31, 2023, 2022 and 2021, respectively, was based on awards granted under the 2012 LTIP, the 2018 LTIP, and the 2020 EIIP. The estimated forfeiture rate as of December 31, 2023 was 8%. Changes in the estimates and assumptions relating to forfeitures may cause the Company to realize material changes in share-based compensation expense in the future. T he amount of unearned share-based compensation related to unvested stock options at December 31, 2023 , is $89.4 million . The weighted-average period over which this unearned share-based compensation is expected to be recognized is 2.43 years. The following table summarizes share-based compensation expense for the periods presented (in thousands): Year Ended 2023 2022 2021 Research and development $ 19,211 $ 14,805 $ 9,514 General and administrative 21,703 16,517 15,144 Total share-based compensation expense $ 40,914 $ 31,322 $ 24,658 The Company recognized tax benefits from share-based awards of $7.2 million, $5.8 million, and $4.7 million, for the years ended December 31, 2023, 2022 and 2021, respectively. With the exception of the options granted on February 12, 2021 pursuant to an option exchange program, where no incremental share-based compensation expense was recognized, the fair value of the options granted to employees and non-employee directors during the years ended December 31, 2023, 2022 and 2021, respectively was estimated as of the grant date using the Black-Scholes option-pricing model assuming the weighted-average assumptions listed in the following table: Year Ended 2023 2022 2021 Expected volatility 81.2 % 82.4 % 81.7 % Risk-free interest rate 4.2 % 2.2 % 1.0 % Expected dividend yield — % — % — % Expected life (in years) 4.8 6.0 6.0 Weighted average grant date fair value $37.32 $23.43 $21.39 The fair value of employee stock options is amortized on a straight-line basis over the requisite service period for each award. Each of the inputs discussed above is subjective and generally requires significant management judgment to determine. The simplified method was used to estimate the expected term of all options in previous years given lack of historical experience. Beginning January 1, 2023, expected term is estimated based on historical experience. The following table summarizes the Company’s stock option activity during the year ended December 31, 2023: Options Weighted Weighted Aggregate Outstanding at December 31, 2022 9,479,998 $ 23.16 6.82 $ 354,856 Granted 1,790,621 56.48 Exercised (1,135,302) 18.90 Forfeited (246,064) 44.28 Expired (22,916) 70.74 Outstanding at December 31, 2023 9,866,337 $ 29.06 6.60 $ 118,447 Vested and expected to vest at December 31, 2023 9,558,866 $ 28.49 6.53 $ 117,705 Vested at December 31, 2023 6,371,511 $ 20.75 5.54 $ 105,546 The total intrinsic value of options exercised was $52.1 million, $49.2 million, and $33.9 million during the years ended December 31, 2023, 2022 and 2021, respectively, determined as of the date of exercise. The following table summarizes the activity and related information for RSUs during the year ended December 31, 2023: Number of Units Weighted Average Weighted Aggregate Unvested at December 31, 2022 23,000 $ 60.89 1.67 $ 1,386 Units Granted 8,000 51.80 Units Vested (5,750) 60.89 Units Forfeited — — Unvested at December 31, 2023 25,250 $ 58.01 1.09 $ 918 Unvested and expected to vest at December 31, 2023 23,066 $ 58.19 1.08 $ 838 The fair value of RSUs was determined on the date of grant based on the market price of the Company’s ordinary shares as of that date. The fair value of the RSUs is recognized as an expense on a straight-line basis over the vesting period of each RSU. Upon the vesting of the RSUs, a portion of the shares vested are sold by the employee to satisfy employee withholding tax requirements (sell-to-cover). The total fair value of shares vested during the year ended December 31, 2023 was $0.2 million. As of December 31, 2023, total compensation cost not yet recognized related to unvested RSUs was $1.0 million, which is expected to be recognized over a weighted-average period of 1.17 years. RSUs settle into ordinary shares upon vesting.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company files its U.S. and Irish income tax returns and income taxes are presented in the Consolidated Financial Statements using the asset and liability method prescribed by the accounting guidance for income taxes. Income (loss) before provision for income taxes by country for each of the fiscal periods presented is summarized as follows (in thousands): Year Ended 2023 2022 2021 Ireland $ (153,920) $ (119,571) $ 65,456 U.S. (6,560) (6,034) 6,465 Income (loss) before provision for income taxes $ (160,480) $ (125,605) $ 71,921 Components of the provision for income taxes for each of the fiscal periods presented consisted of the following (in thousands): Year Ended 2023 2022 2021 Current: U.S. Federal $ 2,200 $ 2,422 $ 356 U.S. State 37 55 16 Ireland — — — Total current provision $ 2,237 $ 2,477 $ 372 Deferred: U.S. Federal $ (15,647) $ (11,039) $ 4,581 U.S. State (42) (94) (7) Ireland — — — Total deferred benefit $ (15,689) $ (11,133) $ 4,574 Provision for (benefit from) income taxes $ (13,452) $ (8,656) $ 4,946 The Company recorded a net tax shortfall (windfall) from stock option exercises of $(3.5) million , $(3.2) million, and $(2.3) million for the years ended December 31, 2023, 2022 and 2021, respectively , all of which were recorded as part of its income tax provision in the Consolidated Statements of Operations. The provision for income taxes differs from the statutory tax rate of 12.5% applicable to Ireland primarily due to Irish net operating losses for which a tax provision benefit is not recognized and U.S. income taxed at different rates. Following is a reconciliation between income taxes computed at the Irish statutory tax rate and the provision for income taxes for each of the fiscal periods presented (in thousands): Year Ended 2023 2022 2021 Taxes at the Irish statutory tax rate of 12.5% $ (20,060) $ (15,700) $ 8,990 Income tax at rates other than applicable statutory rate (7,072) (2,338) (398) Change in valuation allowance 22,406 22,681 4,108 Share-based payments 615 518 5,173 Tax credits (9,382) (8,949) (5,355) Income not subject to tax — (5,000) (7,587) Other 41 132 15 Provision for (benefit from) income taxes $ (13,452) $ (8,656) $ 4,946 Deferred income taxes reflect the net tax effect of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s net deferred tax assets as of December 31, 2023, and 2022 are as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 156,046 $ 136,487 Tax credits 23,728 23,193 Lease liability 2,686 1,398 Accruals and other 1,887 1,587 Capitalized R&D 25,067 10,544 Share-based compensation 9,364 7,628 Gross deferred tax assets 218,778 180,837 Valuation allowance (181,713) (161,098) Net deferred tax assets 37,065 19,739 Deferred tax liability: Operating lease right-of-use assets (2,706) (1,355) Fixed Assets (466) (180) Net deferred tax assets $ 33,893 $ 18,204 The Company's deferred tax assets (“DTA”) are composed primarily of its Irish subsidiaries' net operating loss carryforwards, state net operating loss carryforwards available to reduce future taxable income of the Company's U.S. subsidiaries, federal and California tax credit carryforwards, share-based compensation, capitalized R&D, and other temporary differences. The Company maintains a valuation allowance against certain U.S. federal and state and Irish deferred tax assets. Each reporting period, the Company evaluates the need for a valuation allowance on its deferred tax assets by jurisdiction. For the year ended December 31, 2023, the Company recorded an increase in DTA of $15.7 million, primarily due to Section 174 R&D Capitalization requirements of $14.5 million, which became effective in 2022. For the year ended December 31, 2022, the Company recorded an increase in DTA of $11.1 million, primarily due to Section 174 R&D Capitalization requirements of $10.5 million, which became effective in 2022. Recognition of deferred tax assets is appropriate when realization of such assets is more likely than not. Based upon the weight of available evidence, especially the uncertainties surrounding the realization of deferred tax assets through future taxable income, the Company believes it is not yet more likely than not that certain deferred tax assets will be fully realizable. Accordingly, the Company has provided a valuation allowance of $181.7 million against its deferred tax assets as of December 31, 2023 , primarily in relation to deferred tax assets arising from Federal and California tax credits and net operating losses. The deferred tax assets recognized net of the valuation allowance, $33.9 million as of December 31, 2023, consisted predominantly of U.S. federal temporary differences. Due to expected future U.S. operating income, the Company expects to realize such deferred tax assets. The net increase of $20.6 million in the valuation allowance during the year ended December 31, 2023, was primarily due to Irish net operating losses. As of December 31, 2023, certain of the Company’s Irish entities had trading loss carryovers of $1.1 billion and non-trading loss carryovers of $24.1 million, each of which can be carried forward indefinitely. Trading losses are available against income from the same trade/trades while non-trading losses (excess management expenses) are available against future investment income in the company in which they arise. In addition, as of December 31, 2023, the Company had state net operating loss carryforwards of approximately $126.2 million, which are available to reduce future taxable income, if any, for the Company’s U.S. subsidiary. If not utilized, the state net operating loss carryforward begins expiring in 2032. The Company also has federal and California research and development credit carryforwards of $17.7 million and $19.4 million, respectively, at December 31, 2023. The Tax Reform Act of 1986 and similar California legislation impose substantial restrictions on the utilization of net operating losses and tax credit carryforwards in the event that there is a change in ownership as provided by Section 382 of the Internal Revenue Code and similar state provisions. Such a limitation could result in the expiration of the net operating loss carryforwards and tax credits before utilization, which could result in increased future tax liabilities. The federal research and development credit carryforwards will expire starting in 2041 if not utilized. The California tax credits can be carried forward indefinitely. Cumulative unremitted earnings of the Company’s U.S. subsidiaries total approximately $175.4 million at December 31, 2023. The Company's U.S. subsidiaries' cash balances at December 31, 2023, are committed for its working capital needs and are considered to be indefinitely invested. As such, no provision for income tax in Ireland has been recognized on undistributed earnings of the Company’s U.S. subsidiaries. The determination of a hypothetical unrecognized deferred tax liability as of December 31, 2023 is not practicable because of the complexity and variety of assumptions necessary to compute the tax. A rec onciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands): 2023 2022 Gross Unrecognized Tax Benefits at January 1 $ 11,564 $ 8,329 Additions for tax positions taken in the current year 2,355 2,243 Additions for tax positions taken in the prior year — 992 Reductions for tax positions taken in the prior year (565) — Gross Unrecognized Tax Benefits at December 31 $ 13,354 $ 11,564 If recognized, none of the Company's unrecognized tax benefits as of December 31, 2023, would reduce its annual effective tax rate, primarily due to corresponding adjustments to its deferred tax valuation allowance. As of December 31, 2023, the Company has not recorded a liability for potential interest or penalties. The Company also does not expect its unrecognized tax benefits to change significantly over the next 12 months. The tax years 2013 to 2023 remain subject to examination by the U.S taxing authorities and the tax years 2018 to 2023 remain subject to examination by the Irish taxing authorities as of December 31, 2023 .

Employee Retirement Plan

Employee Retirement Plan	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Employee Retirement Plan	Employee Retirement Plan In the U.S., the Company provides a qualified retirement plan under section 401(k) of the Internal Revenue Code (the “IRC”) under which participants may contribute up to 100% of their eligible compensation, subject to maximum deferral limits specified by the IRC. In addition, the Company contributes 3% of each participating employee’s eligible compensation, subject to limits specified by the IRC, on a quarterly basis. Further, the Company may make an annual discretionary matching and/or profit-sharing contribution as determined solely by the Company. The Company recorded total expense for matching contributions of $1.7 million, $1.3 million and $0.9 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net income (loss)	$ (147,028)	$ (116,949)	$ 66,975

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Preparation and Presentation of Financial Information	Basis of Preparation and Presentation of Financial Information These Consolidated Financial Statements have been prepared in accordance with the accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). These Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Consolidated Financial Statements of Prothena Corporation plc are presented in U.S. dollars, which is the functional currency of the Company and its consolidated subsidiaries. Monetary assets and liabilities denominated in foreign currency are remeasured at period-end exchange rates. Foreign currency gains and losses resulting from remeasurement are recognized in other expense, net in the Consolidated Statements of Operations.
Use of Estimates	Use of Estimates The preparation of the Consolidated Financial Statements in conformity with U.S. GAAP requires the Company to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosures. On an ongoing basis, management evaluates its estimates, including critical accounting policies or estimates related to revenue recognition and research and development expenses. Th e Company bases its estimates on historical experience and on various other market specific and other relevant assumptions that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments held at financial institutions, such as commercial paper, money market funds, and other money market securities with original maturities of three months or less at date of purchase to be cash equivalents. Cash accounts that are restricted to withdrawal or usage are presented as restricted cash. As of December 31, 2023, the Company had $2.2 million of restricted cash held by a bank in certificates of deposit as collateral to standby letters of credit under certain operating leases. See Note 6, "Commitments and Contingencies" for additional information regarding the Company’s operating leases.
Accounts Receivable	Accounts Receivable
Property and Equipment, net	Property and Equipment, net
Impairment of Long-lived Assets	Impairment of Long-lived Assets
Leases	Leases The Company leases both real property and certain equipment for use in its operations. A determination is made as to whether an arrangement is a lease at inception. If so, the Company evaluates the lease agreement to determine whether the lease is an operating or finance lease using the criteria in ASC 842. The Company does not recognize right-of-use assets and lease liabilities that arise from short-term leases for any class of underlying assets. When lease agreements also require the Company to make additional payments for taxes, insurance and other operating expenses incurred during the lease period, such payments are expensed as incurred. See Note 6, “Commitments and Contingencies,” which provides additional details on the Company's current lease arrangements. As of December 31, 2023 and 2022, the Company had no financing leases. Operating leases are included in the operating lease right-of-use (“ROU”) assets, lease liability, current and lease liability, non-current in the Company's Consolidated Balance Sheets. Operating lease ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of all lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on information available at the lease commencement date. The operating lease ROU assets also include any lease prepayments made and exclude lease incentives such as rent abatements and/or concessions and rent holidays. The Company does not assume renewals in its determination of the lease term unless the renewals are deemed by management to be reasonably certain at lease inception. Tenant improvements made by the Company as a lessee in which they are deemed to be owned by the lessor is viewed as lease prepayments by the Company and included in the operating lease ROU assets upon commencement of the lease prior to which they are recorded as prepaid assets. Lease expense for operating leases is recognized on a straight-line basis over the expected lease term as an operating expense. For lease agreements that include lease and non-lease components, such components are generally accounted for separately.
Revenue Recognition	Revenue Recognition The Company’s collaboration revenue includes revenue recognized for milestone payments and reimbursements under the Company’s License Agreement with Roche as well as revenue recognized under the Company’s Collaboration Agreement with BMS. The Company’s l icense and intellectual property revenue includes revenue from Novo Nordisk for the sale of intellectual property and related rights to the Company’s ATTR amyloidosis business and pipeline and milestones payments. The Company analyzes its collaboration arrangements to assess whether they are financing arrangement within the scope of ASC 730 or as a collaboration arrangement pursuant to ASC 808, or whether such arrangements are reflective of a vendor-customer relationship and therefore within the scope of Topic 606. As of December 31, 2023, t he Company has not had any arrangements outside the scope of Topic 606. The following describes the Company’s accounting treatment pursuant to Topic 606: License, Option and Collaboration Revenue The terms of license, option and collaboration agreements entered into typically include payment of one or more of the following: non-refundable, up-front license fees; option exercise fees; development, regulatory and commercial milestone payments; payments for manufacturing supply and research and development services and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities recorded as deferred revenue in the Company’s Consolidated Balance Sheets. At contract inception, for contracts that contain multiple performance obligations, such as the Company’s License Agreement with Roche and the Collaboration Agreement with BMS, the Company accounts for the individual performance obligations separately if they are distinct. Factors considered in the determination of whether the license performance obligations are distinct included, among other things, the research and development capabilities of each of Roche and BMS and their respective sublicense rights, and for the remaining performance obligations the fact that they are not proprietary and can be and have been provided by other vendors. The transaction price is allocated to the separate performance obligation on a relative standalone selling price basis. Revenue is recognized only when the Company satisfies an identified performance obligation by transferring a promised good or service to a customer (in th e Compan y’s case, Roche and BMS). An asset is transferred when, or as, the customer obtains control of that asset, which for a service is considered to be as the services are received and used. The Company recognizes revenue over time by measuring the progress toward complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. Milestone Revenue The Company generally classifies each of its milestones into one of three categories: (i) clinical milestones; (ii) regulatory and development milestones; and (iii) commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research. For example, a milestone payment may be due to the Company upon the initiation of a clinical trial for a new indication. Regulatory and development milestones are typically achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the FDA or other regulatory authorities. For example, a milestone payment may be due to the Company upon submission for marketing approval of a product candidate by the FDA. Commercial milestones are typically achieved when an approved product reaches certain defined levels of net royalty sales by the licensee of a specified amount within a specified period. At the inception of each arrangement that includes developmental, regulatory or commercial milestone payments, the Company evaluates whether achieving the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone (such as a regulatory submission by the Company) is included in the transaction price. Milestone payments that are not within the control of the Company, such as approvals from regulators or where attainment of the specified event is dependent on the development activities of a third party, are not considered probable of being achieved until those approvals are received or the specified event occurs. The Company considers such milestone payments as variable consideration with constraint and therefore recognizes the revenue from such milestone payments as collaboration revenue at point in time when the Company can conclude it is probable that a significant revenue reversal will not occur in future periods. Taxes, Shipping and Handling The Company excludes from the measurement of the transaction price all taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction and collected by the Company from a customer (e.g., sales, use, value added, some excise taxes). In addition, the Company accounts for shipping and handling as activities that are performed after its customers obtain control of the goods as activities to fulfill our performance obligation to transfer the goods.
Research and Development	Research and Development Research and development costs are expensed as incurred. Such costs include, but are not limited to, salaries and benefits, share-based compensation, costs related to preclinical and clinical trial activities including fees paid to clinical research organizations and investigative sites, costs related to drug development and manufacturing prior to regulatory approval for commercial sale, and consulting fees. There can be judgment involved in measuring the research and development expenses to be recognized in a particular period. The level of judgment varies based on the nature of the services being performed and the underlying support obtained. The Company recognizes costs for certain development activities, such as clinical trials, based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by our vendors on their actual costs incurred. For certain clinical trials, expense is recorded based on information obtained from vendors as an intermediary to those performing the underlying services, such as contract research organizations. These estimates are inherently more judgmental because the quality and availability of the underlying data may vary. The Company recognizes costs for contract manufacturing based on evaluation of the progress to completion of specific tasks. The objective of the Company’s accrual policy is to match the recording of the expenses in the Consolidated Financial Statements to the actual services the Company has received and efforts expended. As such, expense accruals related to clinical trials and contract manufacturing are recognized based on the Company’s estimate of the degree of completion of the events specified in the specific clinical study or trial contract or drug development and manufacturing contract, respectively. The Company does not make significant estimates where costs incurred are supported by invoices or reports of costs incurred are obtained from a vendor that is directly performing the underlying services, such as a consultant or contract manufacturing organization. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the Consolidated Financial Statements as prepaid or accrued research and development. Amounts due may be fixed fee, fee for service, and may include upfront payments, monthly payments, and payments upon the completion of milestones or receipt of deliverables. Nonrefundable advance payments for goods and services that will be used or received in future research and development activities are deferred and recognized as expense in the period in which the related goods are delivered or services are performed. The Company has acquired and may continue to acquire the rights to develop and commercialize new drug candidates from third parties. The upfront payments to acquire license, product or rights, as well as any future milestone payments, are immediately recognized as research and development expense provided that the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use.
Share-based Compensation	Share-based Compensation The Company’s share-based compensation programs include options for the purchase of shares and restricted share units (RSUs). Such awards may be granted to employees, directors, and non-employee service providers. The Company measures compensation expense for all share-based awards at the grant date based on the fair value measurement of the award. Share-based compensation expense is recognized on a straight-line basis over the requisite service period, which is generally the vesting period, for each award. The fair value of RSUs is based on the closing market price of the Company’s ordinary shares on the date of grant. To determine the fair value of options for the purchase of shares, the Company uses the Black-Scholes option-pricing model. The determination of fair value using the Black-Scholes option-pricing model is affected by the Company’s share price as well as assumptions regarding a number of complex and subjective variables. Judgment is required in determining the assumptions used in these models which include the risk-free interest rate, expected term, expected volatility and expected dividend yield. The Company uses its historical volatility for the Company's shares to estimate expected volatility. The simplified method has been used to estimate the expected term of all options in previous years. Beginning January 1, 2023, expected term is estimated based on historical experience. Share-based compensation expense recognized in the Consolidated Statements of Operations is based on awards expected to vest and therefore the amount of expense has been reduced for estimated forfeitures which are based on historical experience. Share-based compensation expense is adjusted in subsequent periods for actual forfeitures. The Company records any excess tax benefits or tax shortfalls from its equity awards in its Consolidated Statements of Operations in the reporting periods in which options for the purchase of shares are exercised or RSUs vest.
Income Taxes	Income Taxes The Company files its own U.S. and foreign income tax returns and income taxes are presented in the Consolidated Financial Statements using the asset and liability method prescribed by the accounting guidance for income taxes. Deferred tax assets (“DTAs”) and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using the enacted tax rates projected to be in effect for the year in which the differences are expected to reverse. Net deferred tax assets are recorded to the extent the Company believes that these assets will more likely than not be realized. In making such determination, all available positive and negative evidence is considered, including scheduled reversals of deferred tax liabilities, recent cumulative earnings/losses by taxing jurisdiction, projected future taxable income, tax planning strategies and recent financial operations. Actual operating results in future years could differ from our current assumptions, judgments and estimates. The Company’s significant tax jurisdictions are Ireland and the United States. Estimates are required in determining the Company’s provision for income taxes. Some of these estimates are based on management’s interpretations of jurisdiction-specific tax laws or regulations. Various internal and external factors may have favorable or unfavorable effects on the future effective income tax rate of the business. These factors include, but are not limited to, changes in tax laws, regulations and/or rates, changing interpretations of existing tax laws or regulations, changes in estimates of prior years’ items, past and future levels of R&D spending, the impact of accounting for share-based compensation, and changes in overall levels of income before taxes. The Company did not recognize certain tax benefits from uncertain tax positions within the provision for income taxes. The tax benefit from an uncertain tax position is recognized only if it is more likely than not the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon settlement. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Interest and penalties related to unrecognized tax benefits are accounted for in income tax expense.
Net Income (Loss) per Ordinary Share	Net Income (Loss) per Ordinary Share Basic net income (loss) per ordinary share is calculated by dividing net income (loss) by the weighted-average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed based on the treasury stock method by dividing net income by the weighted-average number of ordinary shares outstanding, plus potentially dilutive ordinary equivalent shares outstanding. However, where there is a net loss, no adjustment is made for potentially issuable ordinary shares because their effect would be anti-dilutive and therefore diluted net loss per share is equal to basic net loss per share.
Comprehensive Loss	Comprehensive Loss Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). The Company has no components of other comprehensive income (loss). Therefore, net income (loss) equals comprehensive income (loss) for all periods presented and, accordingly, the Consolidated Statements of Comprehensive Income (Loss) is not presented in a separate statement.
Segment	The Company operates in one segment. The Company’s chief operating decision maker (the “CODM”), its Chief Executive Officer, manages the Company’s operations and evaluates the Company’s financial performance on a consolidated basis for purposes of allocating resources.
Concentration of Risks	Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and accounts receivable. The Company places its cash equivalents with high credit quality financial institutions and, by policy, limits the amount of credit exposure with any one financial institution. Deposits held with banks have exceeded, and will continue to exceed, federally insured limits. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash and cash equivalents. The Company has not experienced any losses on its deposits of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's Consolidated Balance Sheet. The Company’s business is primarily conducted in U.S. dollars except for its agreements with contract manufacturers for drug supplies which are primarily denominated in Euros. The Company recorded a loss on foreign currency exchange rate differences of approximately $458,000, $397,000 and $96,000 during the years ended December 31, 2023, 2022 and 2021, respectively. If the Company increases its business activities that require the use of foreign currencies, it may be exposed to losses if the Euro and other such currencies continue to strengthen against the U.S. dollar. As of December 31, 2023, and 2022, $3.8 million and $1.7 million, respectively, of the Company’s property and equipment, net were held in the U.S. and a nominal amount were in Ireland. The Company does not own or operate facilities for the manufacture, packaging, labeling, storage, testing or distribution of nonclinical or clinical supplies of any of its drug candidates. The Company instead contracts with and relies on third-parties to manufacture, package, label, store, test and distribute all preclinical development and clinical supplies of our drug candidates, and it plans to continue to do so for the foreseeable future. The Company also relies on third-party consultants to assist in managing these third-parties and assist with its manufacturing strategy.
Recent Accounting Pronouncements	Recent Accounting Pronouncements On November 27, 2023, the FASB issued Accounting Standards Update 2023-07 ("ASU 2023-07"), Segment Reporting- Improvements to Reportable Segment Disclosures, which requires public entities to provide disclosures on significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit or loss and other segment items on an annual and interim basis. The guidance also requires public entities to provide all disclosures about reportable segment’s profit or loss and assets in interim periods that are currently required annually. Public entities with a single reportable segment have to provide all disclosures required by Accounting Standards Codification (ASC) 280, Segment Reporting including the significant segment expense disclosures. The guidance is applied retrospectively to all periods presented in financial statements and is effective for fiscal years beginning after December 15, 2023, and for interim periods beginning after December 15, 2024. Early adoption is permitted. In December 2023, the FASB issued ASU 2023-09, Improvements to Income Tax Disclosures, which requires public business entities to disclose a tabular reconciliation using both percentages and amounts, broken out into specific categories with certain reconciling items at or above 5% of the expected tax further broken out by nature and/or jurisdiction. The guidance also requires all entities to disclose income taxes paid, net of refunds, disaggregated by federal (national), state and foreign taxes for annual periods and to disaggregate the information by jurisdiction based on a quantitative threshold. All entities are required to apply the guidance prospectively, with the option to apply it retrospectively. The guidance is effective for the Company’s fiscal year beginning January 1, 2025. Early adoption is permitted.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Property and Equipment	Depreciation and amortization periods for the Company’s property, plant and equipment are as follows: Asset Estimated Useful Life Machinery and equipment 4-7 years Leasehold improvements Shorter of expected useful life or lease term Purchased computer software 4 years Property and equipment, net consisted of the following (in thousands): December 31, 2023 2022 Machinery and equipment $ 9,019 $ 9,901 Leasehold improvements — 1,498 Purchased computer software 2,232 1,500 11,251 12,899 Less: accumulated depreciation and amortization (7,415) (11,168) Property and equipment, net $ 3,836 $ 1,731

Composition of Certain Balanc_2

Composition of Certain Balance Sheet Items (Tables)	12 Months Ended
	Dec. 31, 2023
Composition of Certain Balance Sheet Items [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid and other current assets consisted of the following (in thousands): December 31, 2023 2022 Prepaid R&D expenses $ 10,998 $ 5,325 Prepaid G&A expenses 803 1,597 Receivable from stock option exercises in-transit — 62 Other 2,140 1,708 Prepaid and other current assets $ 13,941 $ 8,692
Schedule of Property and Equipment	Depreciation and amortization periods for the Company’s property, plant and equipment are as follows: Asset Estimated Useful Life Machinery and equipment 4-7 years Leasehold improvements Shorter of expected useful life or lease term Purchased computer software 4 years Property and equipment, net consisted of the following (in thousands): December 31, 2023 2022 Machinery and equipment $ 9,019 $ 9,901 Leasehold improvements — 1,498 Purchased computer software 2,232 1,500 11,251 12,899 Less: accumulated depreciation and amortization (7,415) (11,168) Property and equipment, net $ 3,836 $ 1,731
Schedule of Other Current Liabilities	Other current liabilities consisted of the following (in thousands): December 31, 2023 2022 Payroll and related expenses $ 13,245 $ 11,060 Professional services 288 605 Other 2,129 503 Other current liabilities $ 15,662 $ 12,168

Net Income (Loss) Per Ordinar_2

Net Income (Loss) Per Ordinary Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Calculation of Basic and Diluted Net Income or Loss Per Ordinary Share	Net income (loss) per ordinary share was determined as follows (in thousands, except per share amounts): Year Ended 2023 2022 2021 Numerator: Net income (loss) $ (147,028) $ (116,949) $ 66,975 Denominator: Weighted-average ordinary shares outstanding used in per share calculations - basic 53,216 47,369 44,228 Dilutive effect of shares issuable under equity incentive plans — — 4,236 Weighted-average ordinary shares outstanding used in per share calculations - diluted 53,216 47,369 48,464 Net income (loss) per share: Basic net income (loss) per ordinary share $ (2.76) $ (2.47) $ 1.51 Diluted net income (loss) per ordinary share $ (2.76) $ (2.47) $ 1.38
Ordinary Shares Equivalent Not Included in Diluted Net Loss Per Share	The equivalent ordinary shares not included in diluted net income (loss) per share because their effect would be anti-dilutive are as follows (in thousands): Year Ended 2023 2022 2021 Stock options to purchase ordinary shares 9,866 9,480 382 Restricted Stock Units (RSU) 25 23 — Total 9,891 9,503 382

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of lease liability maturity analysis and future minimum rentals to be received	Future minimum payments under the above-described noncancelable operating leases, including a reconciliation to the lease liabilities recognized in the Consolidated Balance Sheets as of December 31, 2023, are as follows (in thousands): Year Ended December 31, Operating Leases 2024 2,833 2025 3,052 2026 3,158 2027 3,269 2028 2,523 Thereafter — Total $ 14,835 Less: Present value adjustment (3,000) Lease liability $ 11,835
Schedule of Contractual Obligations by Fiscal Year Maturity	The following is a summary of the Company's non-cancelable purchase commitments and contractual obligations as of December 31, 2023 (in thousands): Total 2024 2025 2026 2027 2028 Thereafter Purchase Obligations (1) $ 12,433 $ 12,397 $ 36 $ — $ — $ — $ — Contractual obligations under license agreements 398 124 64 60 60 45 45 Total $ 12,831 $ 12,521 $ 100 $ 60 $ 60 $ 45 $ 45 ________________ (1) Purchase obligations consist of non-cancelable purchase commitments to suppliers and contract research organizations.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Summary of Share-Based Compensation Expense	The following table summarizes share-based compensation expense for the periods presented (in thousands): Year Ended 2023 2022 2021 Research and development $ 19,211 $ 14,805 $ 9,514 General and administrative 21,703 16,517 15,144 Total share-based compensation expense $ 40,914 $ 31,322 $ 24,658
Fair Value of Options Granted	With the exception of the options granted on February 12, 2021 pursuant to an option exchange program, where no incremental share-based compensation expense was recognized, the fair value of the options granted to employees and non-employee directors during the years ended December 31, 2023, 2022 and 2021, respectively was estimated as of the grant date using the Black-Scholes option-pricing model assuming the weighted-average assumptions listed in the following table: Year Ended 2023 2022 2021 Expected volatility 81.2 % 82.4 % 81.7 % Risk-free interest rate 4.2 % 2.2 % 1.0 % Expected dividend yield — % — % — % Expected life (in years) 4.8 6.0 6.0 Weighted average grant date fair value $37.32 $23.43 $21.39
Summary of Company's Share Option Activity	The following table summarizes the Company’s stock option activity during the year ended December 31, 2023: Options Weighted Weighted Aggregate Outstanding at December 31, 2022 9,479,998 $ 23.16 6.82 $ 354,856 Granted 1,790,621 56.48 Exercised (1,135,302) 18.90 Forfeited (246,064) 44.28 Expired (22,916) 70.74 Outstanding at December 31, 2023 9,866,337 $ 29.06 6.60 $ 118,447 Vested and expected to vest at December 31, 2023 9,558,866 $ 28.49 6.53 $ 117,705 Vested at December 31, 2023 6,371,511 $ 20.75 5.54 $ 105,546
Summary of RSU Activity	The following table summarizes the activity and related information for RSUs during the year ended December 31, 2023: Number of Units Weighted Average Weighted Aggregate Unvested at December 31, 2022 23,000 $ 60.89 1.67 $ 1,386 Units Granted 8,000 51.80 Units Vested (5,750) 60.89 Units Forfeited — — Unvested at December 31, 2023 25,250 $ 58.01 1.09 $ 918 Unvested and expected to vest at December 31, 2023 23,066 $ 58.19 1.08 $ 838

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income (Loss) Before Provision for Income Taxes by Country	Income (loss) before provision for income taxes by country for each of the fiscal periods presented is summarized as follows (in thousands): Year Ended 2023 2022 2021 Ireland $ (153,920) $ (119,571) $ 65,456 U.S. (6,560) (6,034) 6,465 Income (loss) before provision for income taxes $ (160,480) $ (125,605) $ 71,921
Components of the Provision for Income Taxes	Components of the provision for income taxes for each of the fiscal periods presented consisted of the following (in thousands): Year Ended 2023 2022 2021 Current: U.S. Federal $ 2,200 $ 2,422 $ 356 U.S. State 37 55 16 Ireland — — — Total current provision $ 2,237 $ 2,477 $ 372 Deferred: U.S. Federal $ (15,647) $ (11,039) $ 4,581 U.S. State (42) (94) (7) Ireland — — — Total deferred benefit $ (15,689) $ (11,133) $ 4,574 Provision for (benefit from) income taxes $ (13,452) $ (8,656) $ 4,946
Reconciliation Between Income Taxes Computed at the Standard Irish Statutory Tax Rate and the Provision for income Taxes	Following is a reconciliation between income taxes computed at the Irish statutory tax rate and the provision for income taxes for each of the fiscal periods presented (in thousands): Year Ended 2023 2022 2021 Taxes at the Irish statutory tax rate of 12.5% $ (20,060) $ (15,700) $ 8,990 Income tax at rates other than applicable statutory rate (7,072) (2,338) (398) Change in valuation allowance 22,406 22,681 4,108 Share-based payments 615 518 5,173 Tax credits (9,382) (8,949) (5,355) Income not subject to tax — (5,000) (7,587) Other 41 132 15 Provision for (benefit from) income taxes $ (13,452) $ (8,656) $ 4,946
Significant Components of Net Deferred Tax Assets	Significant components of the Company’s net deferred tax assets as of December 31, 2023, and 2022 are as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 156,046 $ 136,487 Tax credits 23,728 23,193 Lease liability 2,686 1,398 Accruals and other 1,887 1,587 Capitalized R&D 25,067 10,544 Share-based compensation 9,364 7,628 Gross deferred tax assets 218,778 180,837 Valuation allowance (181,713) (161,098) Net deferred tax assets 37,065 19,739 Deferred tax liability: Operating lease right-of-use assets (2,706) (1,355) Fixed Assets (466) (180) Net deferred tax assets $ 33,893 $ 18,204
Summary of Income Tax Contingencies	A rec onciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands): 2023 2022 Gross Unrecognized Tax Benefits at January 1 $ 11,564 $ 8,329 Additions for tax positions taken in the current year 2,355 2,243 Additions for tax positions taken in the prior year — 992 Reductions for tax positions taken in the prior year (565) — Gross Unrecognized Tax Benefits at December 31 $ 13,354 $ 11,564

Organization - Additional Infor

Organization - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (980,031)	$ (833,003)
Cash and cash equivalents	$ 618,830	$ 710,406	$ 579,094

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Restricted Cash (Details) $ in Millions	Dec. 31, 2023 USD ($)
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 2.2

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property, Plant, and Equipment (Details)	Dec. 31, 2023
Purchased computer software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	4 years
Minimum | Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	4 years
Maximum | Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life (in years)	7 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Segment and Concentration of Risks (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Concentration Risk [Line Items]
Number of operating segments | segment	1
Loss on foreign currency translation	$ 458	$ 397	$ 96
Property and equipment, net	3,836	1,731
UNITED STATES
Concentration Risk [Line Items]
Property and equipment, net	3,836	1,731
IRELAND
Concentration Risk [Line Items]
Property and equipment, net	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Level 1
Fair Value Inputs, Assets, Quantitative Information
Money market funds at carrying value	$ 589.9	$ 599.1

Composition of Certain Balanc_3

Composition of Certain Balance Sheet Items - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid R&D expenses	$ 10,998	$ 5,325
Prepaid G&A expenses	803	1,597
Receivable from stock option exercises in-transit	0	62
Other	2,140	1,708
Prepaid and other current assets	$ 13,941	$ 8,692

Composition of Certain Balanc_4

Composition of Certain Balance Sheet Items - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Composition of Certain Balance Sheet Items [Abstract]
Machinery and equipment	$ 9,019	$ 9,901
Leasehold improvements	0	1,498
Purchased computer software	2,232	1,500
Property and equipment, gross	11,251	12,899
Less: accumulated depreciation and amortization	(7,415)	(11,168)
Property and equipment, net	$ 3,836	$ 1,731

Composition of Certain Balanc_5

Composition of Certain Balance Sheet Items - Schedule of Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Composition of Certain Balance Sheet Items [Abstract]
Payroll and related expenses	$ 13,245	$ 11,060
Professional services	288	605
Other	2,129	503
Other current liabilities	$ 15,662	$ 12,168

Composition of Certain Balanc_6

Composition of Certain Balance Sheet Items - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Gain on disposition of property and equipment		$ (15)	$ (1)	$ 0
Depreciation expense		900	$ 700	$ 1,100
South San Francisco, CA
Property, Plant and Equipment [Line Items]
Net book value of disposed property and equipment	$ 15
Gain on disposition of property and equipment		$ 22

Net Income (Loss) Per Ordinar_3

Net Income (Loss) Per Ordinary Share - Calculation of Basic and Diluted Net Income or Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income (loss)	$ (147,028)	$ (116,949)	$ 66,975
Denominator:
Weighted Average Number of Shares Outstanding, Basic	53,216	47,369	44,228
Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements	0	0	4,236
Weighted Average Number of Shares Outstanding, Diluted	53,216	47,369	48,464
Net income (loss) per share:
Earnings Per Share, Basic	$ (2.76)	$ (2.47)	$ 1.51
Earnings Per Share, Diluted	$ (2.76)	$ (2.47)	$ 1.38

Net Income (Loss) Per Ordinar_4

Net Income (Loss) Per Ordinary Share - Ordinary Shares Equivalent Not Included in Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equivalent ordinary shares not included in diluted net income (loss) per share (in shares)	9,891	9,503	382
Stock options to purchase ordinary shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equivalent ordinary shares not included in diluted net income (loss) per share (in shares)	9,866	9,480	382
Restricted Stock Units (RSU)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equivalent ordinary shares not included in diluted net income (loss) per share (in shares)	25	23	0

Commitment and Contingencies -

Commitment and Contingencies - Lease Narrative (Details)			1 Months Ended	12 Months Ended
	Oct. 28, 2022 USD ($) ft²	Jul. 18, 2018 ft²	Mar. 31, 2016 ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 31, 2023 USD ($)	Apr. 19, 2023	Apr. 11, 2023	Aug. 01, 2021
Lease Description [Line Items]
Operating Lease (Area) | ft²			128,751
Operating lease right-of-use assets				$ 12,162,000	$ 6,277,000
Operating lease cost				6,300,000	6,300,000	$ 6,300,000
Operating lease payments				6,500,000	6,300,000	6,200,000
Restricted cash				2,200,000
Area of sub-sublease rental | ft²		46,641
Sublease Income				2,800,000	$ 2,900,000	$ 2,900,000
Operating lease, future minimum payment due				$ 14,835,000
Dublin, Ireland
Lease Description [Line Items]
Operating leases, term of contract (in years)								1 year		1 year
Lessee, Operating Lease, Renewal Term									1 year
Brisbane, California
Lease Description [Line Items]
Operating Lease (Area) | ft²	31,157
Operating lease, weighted average remaining lease term				4 years 9 months
Operating lease right-of-use assets							$ 11,400,000
Operating lease cost				$ 1,300,000
Operating lease payments				400,000
Discount rate, percent							5.76%
Tenant improvement allowance	$ 9,300,000
Operating lease, future minimum payment due	14,900,000
Lease liability							$ 3,600,000
Proceeds from tenant allowance				8,200,000
Standby Letters of Credit | Brisbane, California
Lease Description [Line Items]
Line of credit has been used				0
Restricted cash	$ 900,000
Standby Letters of Credit | South San Francisco, CA
Lease Description [Line Items]
Line of credit has been used				0
Restricted cash				$ 1,400,000

Commitment and Contingencies _2

Commitment and Contingencies - Schedule of Lease Liability Maturity Analysis and Future Minimum Rentals to be Received (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Operating Leases
2024	$ 2,833
2025	3,052
2026	3,158
2027	3,269
2028	2,523
Thereafter	0
Total	14,835
Less: Present value adjustment	(3,000)
Lessee, Operating Lease, Liability	$ 11,835

Commitment and Contingencies _3

Commitment and Contingencies - Commitment Narrative (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Long-term Purchase Commitment [Line Items]
Purchase obligation	$ 12,433	[1]
Contractual obligation	400
Current liabilities
Long-term Purchase Commitment [Line Items]
Commitment to suppliers included in current liabilities	6,300
Contractual obligations under license agreements included in current liabilities	$ 60
[1] Purchase obligations consist of non-cancelable purchase commitments to suppliers and contract research organizations.

Commitment and Contingencies _4

Commitment and Contingencies - Contractual Obligations (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Purchase Obligations
Total	$ 12,433	[1]
2024	12,397	[1]
2025	36	[1]
2026	0	[1]
2027	0	[1]
2028	0	[1]
Thereafter	0	[1]
Contractual obligations under license agreements
Total	400
Total
Total	12,831
2024	12,521
2025	100
2026	60
2027	60
2028	45
Thereafter	45
License Agreements
Contractual obligations under license agreements
Total	398
2024	124
2025	64
2026	60
2027	60
2028	45
Thereafter	$ 45
[1] Purchase obligations consist of non-cancelable purchase commitments to suppliers and contract research organizations.

Significant Agreements - Roche

Significant Agreements - Roche License Agreement (Details) - USD ($)		1 Months Ended			12 Months Ended
	May 05, 2021	Jun. 30, 2017	May 31, 2014	Feb. 28, 2014	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
License Agreement [Line Items]
Collaboration revenue					$ 91,370,000	$ 53,905,000	$ 200,577,000
Accounts receivable					5,159,000	0
Collaboration revenue
License Agreement [Line Items]
Collaboration revenue					$ 91,320,000	13,855,000	139,833,000
Collaborative Arrangement
License Agreement [Line Items]
Portion of revenue and expenses attributable to company, percentage					30%
Roche
License Agreement [Line Items]
Revenue, Remaining Performance Obligation, Amount					$ 0	0
Roche | Collaboration revenue
License Agreement [Line Items]
Collaboration revenue					0	0	60,200,000
Roche | Collaborative Arrangement
License Agreement [Line Items]
Upfront payment pursuant to license agreement				$ 30,000,000
Milestone payment received, clinical milestone			$ 15,000,000
Milestone achievement, clinical milestone	$ 60,000,000	$ 30,000,000
Potential payment upon achievement of development, regulatory and various first commercial sales milestones					290,000,000
Potential payment for achievement of non U.S.commercial sales milestones					$ 175,000,000
Cost allocation, percentage					100%
Portion of revenue and expenses attributable to company, percentage					70%
Potential alternative commercial sales milestone					$ 155,000,000
Cost sharing payments recognized as research and development expense					0	0	$ 7,200,000
Accounts receivable					$ 0	$ 0

Significant Agreements - Bristo

Significant Agreements - Bristol Myers Squibb Collaboration Agreement (Details)				12 Months Ended
	Jul. 05, 2023 USD ($)	Jul. 30, 2021 USD ($)	Mar. 20, 2018 USD ($) agreement_term $ / shares shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, current				$ 0	$ 11,442,000
Collaboration revenue				91,370,000	53,905,000	$ 200,577,000
Accounts receivable				5,159,000	0
Deferred revenue, non-current				67,405,000	85,293,000
Collaboration Program, US Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Potential Regulatory Milestone Payments Per Program			$ 90,000,000
Collaboration Agreement, Potential Commercial Milestone Payments Per Program			375,000,000
Collaboration Program, US Rights | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Expected Allocation of Initial Transaction Price			15,000,000
Collaboration Program, US Rights | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Expected Allocation of Initial Transaction Price			25,000,000
Collaboration Program, Global Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Potential Regulatory Milestone Payments Per Program			187,500,000
Collaboration Agreement, Potential Commercial Milestone Payments Per Program			375,000,000
Collaboration Program, Global Rights | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Expected Allocation of Initial Transaction Price			10,000,000
Collaboration Program, Global Rights | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Expected Allocation of Initial Transaction Price			18,000,000
Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue				91,320,000	13,855,000	139,833,000
BMS (formerly Celgene)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Upfront Payment			$ 100,000,000
Collaboration Agreement, Option Fees and Milestone Payments, Payment Term			30 days
BMS (formerly Celgene) | Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Share Subscription Agreement, Number of Ordinary Shares Issued in Transaction | shares			1,174,536
Share subscription agreement, price per share (in dollars per share) | $ / shares			$ 42.57
Share subscription agreement, consideration received on transaction			$ 50,000,000
Share Subscription Agreement, Premium Received on Transaction			10,200,000
Bristol Myers Squibb
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Potential Regulatory and Commercial Milestone Payments Per Program			$ 562,500,000
Collaboration Agreement, Term of Agreement			6 years
Collaboration Agreement, Number of Additional 12 Month Period Extension Allowed | agreement_term			2
Collaboration Agreement, Extension Fee per Extension Period			$ 10,000,000
Collaboration revenue				91,300,000		79,700,000
Deferred Revenue				67,400,000	96,700,000
Bristol Myers Squibb | Collaboration Program, US Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, exercise fee per program			80,000,000
Bristol Myers Squibb | Collaboration Program, Global Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, exercise fee per program			55,000,000
Bristol Myers Squibb | Collaboration Revenue, US License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue						77,500,000
Allocated consideration to performance obligations		$ 77,500,000
Bristol Myers Squibb | Collaboration Revenue, US Development Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue					13,900,000	$ 2,200,000
Allocated consideration to performance obligations		27,500,000
Bristol Myers Squibb | Collaboration Program, US, Tau/ PRX005
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Allocation of Initial Transaction Price			24,900,000
Collaboration Agreement, Total Transaction Price, PRX005 US		104,900,000
Collaboration Program, US License Agreement, Upfront Payment		$ 80,000,000
Bristol Myers Squibb | Collaboration Program, Global, tau/ BMS-986446
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Agreement, Potential Regulatory and Commercial Milestone Payments Per Program	$ 562,500,000
Collaboration Agreement, Allocation of Initial Transaction Price	17,900,000
Collaboration Agreement, Total Transaction Price, PRX005 Global	72,900,000
Collaboration Program, Global Exercise Fee	$ 55,000,000
Bristol Myers Squibb | Collaboration Revenue, Supply Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration Revenue, Transaction Price				4,700,000
Collaborative Arrangement | BMS (formerly Celgene)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, Initial transaction price			$ 110,200,000
Collaborative Arrangement | Bristol Myers Squibb
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable				5,200,000	$ 0
Revenue, Remaining Performance Obligation, Amount				0
Collaboration Program, Global, tau/ BMS-986446 | Bristol Myers Squibb
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue				$ 11,400,000

Significant Agreements - Novo N

Significant Agreements - Novo Nordisk Share Purchase Agreement (Details) - USD ($)		1 Months Ended	12 Months Ended
	Jul. 08, 2021	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable		$ 0	$ 5,159,000	$ 0
Accounts Receivable, after Allowance for Credit Loss			0
Novo Nordisk
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Share Purchase Agreement, Upfront Payment	$ 60,000,000
Share Purchase Agreement, Potential Payment Upon Achievement of Development and Sales Milestones			1,130,000,000
Revenue from License and Intellectual Property, Share Purchase Agreement			$ 0	(40,000,000)	$ (60,700,000)
Milestone achievement, clinical milestone		40,000,000
Accounts Receivable, after Allowance for Credit Loss		$ 0		$ 0
Novo Nordisk | Transition services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from License and Intellectual Property, Share Purchase Agreement	$ 700,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 vote € / shares shares	Dec. 31, 2023 $ / shares shares	Dec. 31, 2022 € / shares shares	Dec. 31, 2022 $ / shares shares
Equity [Abstract]
Ordinary shares, number of authorized shares (in shares)	100,000,000	100,000,000	100,000,000	100,000,000
Ordinary shares, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Ordinary shares, number of outstanding shares (in shares)	53,682,117	53,682,117	52,103,608	52,103,608
Ordinary shares, number of issued shares (in shares)	53,682,117	53,682,117	52,103,608	52,103,608
Votes per share | vote	1
Ordinary shares, number of shares reserved for future issuance (in shares)	13,477,039	13,477,039
Euro deferred shares, number of shares authorized (in shares)	10,000	10,000	10,000	10,000
Euro deferred shares, nominal value (in euros per share) | € / shares	€ 22		€ 22
Euro deferred shares, number of outstanding shares (in shares)	0	0

Shareholders' Equity - March 20

Shareholders' Equity - March 2021 Offering (Details) - Underwritten Public Offering - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended
	Jan. 18, 2023	Dec. 19, 2022	Mar. 31, 2021
Shareholders Equity [Line Items]
Shares issued, price per share (in dollars per share)		$ 56.50	$ 20.75
Ordinary Shares
Shareholders Equity [Line Items]
Issuance of ordinary shares (in shares)	395,096	3,250,000	4,025,000
Proceeds from issuance of ordinary shares in public offering, net	$ 20,900		$ 78,000

Shareholders' Equity - December

Shareholders' Equity - December 2022 Offering (Details) - Underwritten Public Offering - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended
	Jan. 18, 2023	Dec. 19, 2022	Mar. 31, 2021
Shareholders Equity [Line Items]
Shares issued, price per share (in dollars per share)		$ 56.50	$ 20.75
Ordinary Shares
Shareholders Equity [Line Items]
Issuance of ordinary shares (in shares)	395,096	3,250,000	4,025,000
Proceeds from issuance of ordinary shares in public offering, net		$ 172,400
Maximum Number Of Shares, Underwriters Option to Purchase	487,500
Proceeds from issuance of ordinary shares in public offering, net	$ 20,900		$ 78,000

Shareholders' Equity - At-the-M

Shareholders' Equity - At-the-Market Offerings (Details) - USD ($)		1 Months Ended	12 Months Ended
	Dec. 23, 2021	May 31, 2021	Dec. 31, 2023	Dec. 31, 2022
May 2021 At-The-Market Offering
Shareholders Equity [Line Items]
Stock Issuance Costs				$ (3,200,000)
December 2021 At-The-Market Offering
Shareholders Equity [Line Items]
Stock Issuance Costs			$ 100,000	$ 1,700,000
Ordinary Shares | May 2021 At-The-Market Offering
Shareholders Equity [Line Items]
Sale of stock, maximum aggregate offering price, value		$ 100,000,000
Issuance of ordinary shares (in shares)				1,640,174
Proceeds from issuance of ordinary shares, gross				$ 100,000,000
Ordinary Shares | December 2021 At-The-Market Offering
Shareholders Equity [Line Items]
Sale of stock, maximum aggregate offering price, value	$ 250,000,000
Issuance of ordinary shares (in shares)			42,361	911,228
Proceeds from issuance of ordinary shares, gross			$ 3,200,000	$ 53,100,000

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail) - USD ($)		12 Months Ended
	May 18, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Payment Arrangement [Line Items]
Grant period (in years)		10 years
Number of shares available for grant (in shares)		3,585,452
Share-based payment arrangement, estimated forfeiture rate		8%
Share-based compensation not yet recognized, stock options		$ 89,400,000
Share-based compensation not yet recognized, period for recognition (in years)		2 years 5 months 4 days
Tax benefit from compensation expense		$ 7,200,000	$ 5,800,000	$ 4,700,000
Restricted Stock Units (RSU)
Share-based Payment Arrangement [Line Items]
Vesting period (in years)		2 years
Share-based compensation not yet recognized, period for recognition (in years)		1 year 2 months 1 day
Fair value of RSU vested		$ 200,000
Compensation cost not yet recognized related to unvested RSU		$ 1,000,000
Option Awards
Share-based Payment Arrangement [Line Items]
Vesting period (in years)		4 years
Intrinsic value of options exercised		$ 52,100,000	$ 49,200,000	$ 33,900,000
Amended and Restated 2018 Long Term Incentive Plan
Share-based Payment Arrangement [Line Items]
Number of additional shares authorized (in shares)	2,000,000
Authorized shares for issuance (in shares)		14,614,183
2020 Employment Inducement Incentive Plan
Share-based Payment Arrangement [Line Items]
Authorized shares for issuance (in shares)		1,485,000
Number of shares available for grant (in shares)		58,750

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 40,914	$ 31,322	$ 24,658
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	19,211	14,805	9,514
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 21,703	$ 16,517	$ 15,144

Share-Based Compensation - Fair

Share-Based Compensation - Fair Value of Options Granted (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement [Abstract]
Expected volatility	81.20%	82.40%	81.70%
Risk-free interest rate	4.20%	2.20%	1%
Expected dividend yield	0%	0%	0%
Expected life (in years)	4 years 9 months 18 days	6 years	6 years
Weighted average grant date fair value (in dollars per share)	$ 37.32	$ 23.43	$ 21.39

Share-based Compensation - Shar

Share-based Compensation - Share-based Compensation Plan - Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-based Payment, Options, Outstanding [Roll Forward]
Options, outstanding beginning balance	9,479,998
Options, granted	1,790,621
Options, exercised	(1,135,302)
Options, forfeited	(246,064)
Options, expired	(22,916)
Options, outstanding ending balance	9,866,337	9,479,998
Options, vested and expected to vest ending balance	9,558,866
Options, vested outstanding number	6,371,511
Share-based Payment, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, outstanding beginning balance (in dollars per share)	$ 23.16
Weighted average exercise price, granted (in dollars per share)	56.48
Weighted average exercise price, exercised (in dollars per share)	18.90
Weighted average exercise price, forfeited (in dollars per share)	44.28
Weighted average exercise price, expired (in dollars per share)	70.74
Weighted average exercise price, outstanding ending balance (in dollars per share)	29.06	$ 23.16
Weighted average exercise price, vested and expected to vest ending balance (in dollars per share)	28.49
Weighted average exercise price, options vested (in dollars per share)	$ 20.75
Share-Based Payment, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual life, outstanding ending balance (in years)	6 years 7 months 6 days	6 years 9 months 25 days
Weighted average remaining contractual life, vested and expected to vest ending balance (in years)	6 years 6 months 10 days
Weighted average remaining contractual term, vested outstanding (in years)	5 years 6 months 14 days
Aggregate intrinsic value, outstanding beginning balance	$ 354,856
Aggregate intrinsic value, outstanding ending balance	118,447	$ 354,856
Aggregate intrinsic value, vested and expected to vest ending balance	117,705
Aggregate intrinsic value, options vested	$ 105,546

Share-based Compensation - Su_2

Share-based Compensation - Summary of RSU Activity (Details) - Restricted Stock Units (RSU) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Units
Restricted stock unit, beginning balance (in shares)	23,000
Restricted stock units granted in period (in shares)	8,000
Restricted stock units vested in period (in shares)	(5,750)
Restricted stock units forfeited (in shares)	0
Restricted stock unit, ending balance (in shares)	25,250	23,000
Restricted stock unit, unvested and expected to vest (in shares)	23,066
RSU, Weighted Average Grant Date Fair Value
Restricted stock units beginning balance (in dollars per share)	$ 60.89
Restricted stock units grant-date fair value (in dollars per share)	51.80
Restricted stock units vested (in dollars per share)	60.89
Restricted stock units forfeited (in dollars per share)	0
Restricted stock units ending balance (in dollars per share)	58.01	$ 60.89
Restricted stock units, unvested and expected to vest (in dollars per share)	$ 58.19
RSU, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term (years)	1 year 1 month 2 days	1 year 8 months 1 day
Weighted average remaining contractual term, unvested and expected to vest (years)	1 year 29 days
Aggregate Intrinsic Value	$ 918	$ 1,386
Aggregate intrinsic value, invested and expected to vest	$ 838

Income Taxes - Income (Loss) Be

Income Taxes - Income (Loss) Before Provision for Income Taxes by Country (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Income (loss) before provision for income taxes	$ (160,480)	$ (125,605)	$ 71,921
Ireland
Income Tax Disclosure [Line Items]
Ireland	(153,920)	(119,571)	65,456
U.S.
Income Tax Disclosure [Line Items]
Foreign	$ (6,560)	$ (6,034)	$ 6,465

Income Taxes - Components of th

Income Taxes - Components of the Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current:
Total Current Provision	$ 2,237	$ 2,477	$ 372
Deferred:
Total Deferred Income Tax Expense (Benefit)	(15,689)	(11,133)	4,574
Provision for (benefit from) income taxes	(13,452)	(8,656)	4,946
U.S.
Current:
U.S. Federal	2,200	2,422	356
Deferred:
U.S. Federal	(15,647)	(11,039)	4,581
U.S. State
Current:
U.S. State	37	55	16
Deferred:
U.S. State	(42)	(94)	(7)
Ireland
Current:
Foreign Federal	0	0	0
Deferred:
Foreign Federal	$ 0	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Tax shortfall (windfall) recorded in tax provision relating to stock compensation	$ (3,500,000)	$ (3,200,000)	$ (2,300,000)
Accumulated deficit	(980,031,000)	(833,003,000)
Valuation allowance	(181,713,000)	(161,098,000)
Deferred tax assets, net	33,893,000	18,204,000
Increase (decrease) in valuation allowance	20,600,000
Deferred Tax Assets, Period Increase (Decrease)	15,700,000	11,100,000
Period increase (decrease) in Deferred Tax Assets, Capitalization Of Research And Development Costs	14,500,000	$ 10,500,000
U.S.
Income Taxes [Line Items]
Undistributed earnings of foreign subsidiaries	$ 175,400,000
Ireland
Income Taxes [Line Items]
Irish Statutory Income Tax Rate, Percent	12.50%
Ireland | Trading Loss Carryover
Income Taxes [Line Items]
Operating loss carryforwards	$ 1,100,000,000
Ireland | Non-Trading Loss Carryover
Income Taxes [Line Items]
Operating loss carryforwards	24,100,000
U.S.
Income Taxes [Line Items]
Research and development credit carryforwards	17,700,000
U.S. State
Income Taxes [Line Items]
Operating loss carryforwards	126,200,000
Research and development credit carryforwards	$ 19,400,000

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Income Taxes Computed at the Standard Irish Statutory Tax Rate and the Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Taxes at the Irish statutory tax rate of 12.5%	$ (20,060)	$ (15,700)	$ 8,990
Income tax at rates other than applicable statutory rate	(7,072)	(2,338)	(398)
Change in valuation allowance	22,406	22,681	4,108
Share-based payments	615	518	5,173
Tax credits	(9,382)	(8,949)	(5,355)
Income not subject to tax	0	(5,000)	(7,587)
Other	41	132	15
Provision for (benefit from) income taxes	$ (13,452)	$ (8,656)	$ 4,946

Income Taxes - Significant Comp

Income Taxes - Significant Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 156,046	$ 136,487
Tax credits	23,728	23,193
Lease liability	2,686	1,398
Accruals and other	1,887	1,587
Capitalized R&D	25,067	10,544
Share-based compensation	9,364	7,628
Gross deferred tax assets	218,778	180,837
Valuation allowance	(181,713)	(161,098)
Net deferred tax assets	37,065	19,739
Deferred tax liability:
Operating lease right-of-use assets	(2,706)	(1,355)
Fixed Assets	(466)	(180)
Net deferred tax assets	$ 33,893	$ 18,204

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits, [Roll Forward]
Gross Unrecognized Tax Benefits at January 1	$ 11,564	$ 8,329
Additions for tax positions taken in the current year	2,355	2,243
Additions for tax positions taken in the prior year	0	992
Reductions for tax positions taken in the prior year	(565)	0
Gross Unrecognized Tax Benefits at December 31	$ 13,354	$ 11,564

Employee Retirement Plan (Detai

Employee Retirement Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
IRELAND
Defined Contribution Plan Disclosure [Line Items]
Companies contribution to each participating employee's eligible compensation (as percent)	7.50%
Recorded expense for employer contributions	$ 152,000	$ 133,000	$ 73,000
UNITED STATES
Defined Contribution Plan Disclosure [Line Items]
Maximum contribution by participants (as percent)	100%
Companies contribution to each participating employee's eligible compensation (as percent)	3%
Recorded expense for employer contributions	$ 1,700,000	$ 1,300,000	$ 900,000