Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 36,151	$ 20,051
Tax credit carryforwards	3,507	2,321
Accrued expenses and other	2,037	1,097
Total deferred tax assets	41,695	23,469
Deferred tax liabilities:
ASC 842 right-of-use asset	(442)
Depreciation and amortization		(10)
Total deferred tax liabilities	(442)	(10)
Valuation allowance	$ (41,253)	$ (23,459)	$ (11,724)