Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation expense
Stock-based compensation expense	$ 26,873	$ 20,730	$ 22,759
Research and development
Stock-based compensation expense
Stock-based compensation expense	10,698	8,833	8,277
General and administrative
Stock-based compensation expense
Stock-based compensation expense	16,175	11,897	14,482
Stock options
Stock-based compensation expense
Stock-based compensation expense	26,873	20,730	22,487
Unvested restricted common stock
Stock-based compensation expense
Stock-based compensation expense	$ 0	$ 0	$ 272

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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