Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

	As of December 31,
	2022		2021
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	251,331	$	229,427
Research and development tax credits	29,290		29,290
Orphan drug credits	24,524		24,524
Capitalized research and development	33,813		36,770
Stock-based compensation	5,445		5,163
Interest	398		148
Other	2,255		1,308
Total deferred tax assets	347,056		326,630
Deferred tax liabilities:
Other	(1,295)		(412)
Total deferred tax liabilities	(1,295)		(412)
Less: valuation allowance	(345,761)		(326,218)
Net deferred tax liabilities	$	—	$	—

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of the statutory tax rate to the effective tax rate for the years ended December 31, 2022, 2021 and 2020 consists of the following:

	Year Ended December 31,
	2022		2021		2020
	(in thousands)
Expected income tax expense (benefit) at 21%	$	(21,408)	$	(18,429)	$	(12,300)
State income taxes, net of federal benefit	—		—		(269)
Equity compensation	1,627		851		1,777
Write off of credit carryover due to 382 study	—		—		31,053
Change in valuation allowance	19,543		17,210		(20,418)
Other (1)	238		368		157
Income tax benefit	$	—	$	—	$	—