Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

	As of December 31,
	2020		2019
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	201,610	$	193,270
Research and development tax credits	29,304		46,306
Orphan drug credits	24,524		24,524
Capitalized research and development	47,075		58,596
Stock-based compensation	5,651		5,340
Other	844		5,533
Total deferred tax assets	309,008		333,569
Deferred tax liabilities:
Deferred tax liability related to acquisition of Symphony Icon	—		(4,140)
Other	—		(3)
Total deferred tax liabilities	—		(4,143)
Less: valuation allowance	(309,008)		(329,426)
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, 2020, 2019 and 2018 consists of the following:

	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Expected income tax expense (benefit) at 21%	$	(12,300)	$	26,065	$	(25,315)
State income taxes, net of federal benefit	(269)		445		(809)
Equity compensation	1,777		1,688		1,059
Research and development credit	—		—		(978)
Write off of credit carryover due to 382 study	31,053		—		—
Change in valuation allowance	(20,418)		(35,276)		25,928
Other (1)	157		1,064		115
Income tax benefit	$	—	$	(6,014)	$	—