Balance Sheet Accounts and Supplemental Disclosures - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued compensation	$ 2,533	$ 4,102
Operating lease liabilities	2,170
Accrued professional service fees	1,318	2,697
Accrued other	1,858	769
Total accrued expenses	$ 7,879	$ 7,568