Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

	As of December 31,
	2021		2020
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	229,427	$	201,610
Research and development tax credits	29,290		29,304
Orphan drug credits	24,524		24,524
Capitalized research and development	36,770		47,075
Stock-based compensation	5,163		5,651
Interest	148		—
Other	1,308		844
Total deferred tax assets	326,630		309,008
Deferred tax liabilities:
Other	(412)		—
Total deferred tax liabilities	(412)		—
Less: valuation allowance	(326,218)		(309,008)
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, 2021, 2020 and 2019 consists of the following:

	Year Ended December 31,
	2021		2020		2019
	(in thousands)
Expected income tax expense (benefit) at 21%	$	(18,429)	$	(12,300)	$	26,065
State income taxes, net of federal benefit	—		(269)		445
Equity compensation	851		1,777		1,688
Write off of credit carryover due to 382 study	—		31,053		—
Change in valuation allowance	17,210		(20,418)		(35,276)
Other (1)	368		157		1,064
Income tax benefit	$	—	$	—	$	(6,014)