Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands		1 Months Ended			12 Months Ended
	Jul. 25, 2017	Jul. 25, 2017	Dec. 31, 2015	Dec. 31, 2011	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies [Line Items]
Future sublease payments receivable from related party					$ 400
Sublease, term of contract					2 years
Rent expense					$ 3	$ 3
San Diego Headquarters
Commitments And Contingencies [Line Items]
Operating lease, agreement period (in years)				5 years
Operating lease, renewal option (in years)				3 years
Operating lease, monthly rent				$ 24
Operating lease, rent expense percentage of annual escalation				3.00%
Operating lease, rent abatement period			6 months
Operating lease, rent abatement recovery period			60 months
Pending Litigation | Majorelle Case | Minimum
Commitments And Contingencies [Line Items]
Loss contingency, damages sought	$ 1,000	$ 1