Income Taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets:
NOL carryforwards	$ 68,802	$ 60,759
Research and development tax credit carryforwards	14,801	14,923
Orphan drug tax credit carryforwards	20,096	18,778	$ 18,100
Depreciation and amortization	7,493	8,478
Capitalized research and development expenditures	37,528	34,832
Stock options	3,344	6,584
Accrued expenses and other	916	708
Oberland agreement	14,637	15,872
Lease liability ASC 842	1,371	1,846
Total gross deferred tax asset	168,988	162,780
Valuation allowance	(167,424)	(160,987)
Net deferred tax asset	1,564	1,793
Deferred tax liabilities:
Right of use asset ASC 842	(1,564)	(1,793)
Total gross deferred tax liabilities	(1,564)	(1,793)
Net deferred tax assets (liabilities)	$ 0	$ 0