Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2018	Feb. 28, 2018	Jan. 31, 2010	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies [Line Items]
Rent expense				$ 0.4	$ 0.4
Malvern, Pennsylvania
Commitments And Contingencies [Line Items]
Lease commencement date			Mar. 31, 2010
Lease extended expiration date		Sep. 30, 2023
Lessee, operating lease, option to extend description				amended to extend its term to September 30, 2023
Lessee, operating lease, existence of option to extend [true false]				true
San Diego, California
Commitments And Contingencies [Line Items]
Lease expiration date	Oct. 31, 2022