Fair Value Measurement - Summary of Assets and Liabilities that Require Fair Value Measurements on a Recurring Basis (Details) - Fair Value Measurements on Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets
Cash equivalents	$ 56,107	$ 27,872
Liabilities
Development derivative liability (Note 8)	94,037	51,719
Level 1
Assets
Cash equivalents	56,107	27,872
Liabilities
Development derivative liability (Note 8)	0	0
Level 2
Assets
Cash equivalents	0	0
Liabilities
Development derivative liability (Note 8)	0	0
Level 3
Assets
Cash equivalents	0	0
Liabilities
Development derivative liability (Note 8)	$ 94,037	$ 51,719

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

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Balance Type:	credit
Period Type:	instant