Income Taxes - Components of Deferred Tax Assets and Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 39,907	$ 27,704
Depreciation and amortization	318	269
Accruals/other	5,454	2,455
Operating lease liability	1,516
Research and development credits & foreign credits	8,038	4,270
Total deferred tax assets	55,233	34,698
Deferred tax liabilities:
Operating right-of-use asset	(1,269)
Total deferred tax liabilities	(1,269)
Valuation allowance	(52,531)	(34,040)
Net deferred tax assets	1,433	658
Valuation allowance
Increase in valuation allowance	$ 18,500	$ 8,200	$ 1,900