Income Taxes - Deferred Assets and Liabilities, CFDs (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 119,155	$ 120,554
Capitalized start-up costs	3,812	5,506
Research and development tax credit carryforwards	20,505	15,233
Section 174 research and development capitalization	30,984	19,639
Capitalized research and development expense	2,359	5,448
Stockbased compensation expense	18,055	19,432
Accrued compensation	1,219	1,146
Lease liabilities	774	558
Other	407	534
Total deferred tax assets	197,270	188,050
Deferred tax liabilities:
Property and equipment	(187)	(137)
Intangible asset		(1,576)
Right-to-use assets	(853)	(651)
Other	(1,106)	(1,365)
Total deferred tax liabilities	(2,146)	(3,729)
Valuation allowance	(195,124)	(184,688)	$ (161,824)	$ (134,559)
Deferred tax liabilities, net		$ (367)
Federal
Deferred tax liabilities:
Operating loss carryforwards	464,800
Federal | Research Tax Credit Carryforward [Member]
Deferred tax liabilities:
Tax credit carryforward	20,400
State
Deferred tax liabilities:
Operating loss carryforwards	395,300
State | Research Tax Credit Carryforward [Member]
Deferred tax liabilities:
Tax credit carryforward	$ 100