Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 46,603	$ 30,444
Research and development credit carryforwards	6,842	4,658
Orphan drug credit carryforwards	3,032
Intangible assets	6,722	7,235
Deferred revenue	1,791
Accrued expenses and other	2,240	1,149
Deferred lease incentive	962	1,090
Deferred rent	450	426
Gross deferred tax assets	68,642	45,002
Valuation allowance	(67,427)	(43,586)
Net deferred tax assets	1,215	1,416
Deferred tax liability	$ (1,215)	$ (1,416)