Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents	$ 12,532		$ 15,430
Restricted cash	1,000		1,000
Cash and restricted balances	13,501	$ 42,919	16,399	$ 23,789
Operating lease right-of-use asset	0		$ 149
Reduction of net cash used in operating activities	(9,016)	(7,233)
Reduction of net cash provided by financing activities	$ (1,277)	(25,763)
Overstatement of Prepayment Fees | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reduction of net cash used in operating activities		3,400
Reduction of net cash provided by financing activities		$ 3,400
Customer Concentration Risk | Genentech, Inc.
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Concentration risk (as a percent)	92.22511%	100.00%