Accrued and Other Current Liabilities - Details of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued clinical trial expenses	$ 14,215	$ 18,666
Accrued compensation	4,930	7,179
Other accrued liabilities	6,622	4,074
Common stock warrant liabilities	36	198
Accrued Liabilities and Other Current Liabilities	$ 25,803	$ 30,117