Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 19,629	$ 5,240
Research and development tax credit carryforwards	6,234	1,945
Deferred revenue	10,543	14,740
Deferred rent		1,376
Intangible assets	430	791
Accrued expenses	843	687
Stock-based compensation	2,414	1,468
Lease liability	5,445
Other	23	73
Total deferred tax assets	45,561	26,320
Valuation allowance	(36,535)	(18,602)	$ (19,956)	$ (11,531)
Deferred tax assets	9,026	7,718
Deferred tax liabilities:
Right-of-use asset	(4,059)
Depreciation	(1,281)	(1,629)
Deferred revenue tax accounting method change	(3,045)	(6,089)
Beneficial conversion feature on convertible note payable	(559)
Other	(82)
Total deferred tax liabilities	$ (9,026)	$ (7,718)