Income Taxes - Deferred Income Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Components of Deferred Tax Assets [Abstract]
Net operating loss carryforwards	$ 65,487	$ 15,482
Research and development tax credit carryforwards	3,654	2,710
Capitalized research and development expenses	2,626	2,837
Capitalized license fees	0	221
Accrual-to-cash basis conversion	0	1,367
Lease liabilities	765	0
Other	1,413	180
Total deferred tax assets	73,945	22,797
Valuation allowance	(73,410)	(22,797)
Deferred tax assets, net of valuation allowance	535	0
Right of use assets	535	0
Total deferred tax liabilities	535	0
Total deferred tax assets, net	$ 0	$ 0