Commitments and Contingencies - Narrative (Details) $ in Millions		2 Months Ended	12 Months Ended
	Jul. 20, 2015	Oct. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) lease	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leased Assets [Line Items]
Number of noncancelable leases | lease			2
Rent expense			$ 1.8	$ 1.9	$ 1.5
Amended Lease Agreement [Member] | Building [Member]
Operating Leased Assets [Line Items]
Additional renewal term	5 years
Emeryville [Member] | Building [Member]
Operating Leased Assets [Line Items]
Base rent increase (percent)			3.00%
Accrued Lease Obligations [Member]
Operating Leased Assets [Line Items]
Cease-use liability		$ 1.1
Derecognized deferred rent liability		0.5
Loss on lease		$ 0.6
Accrued operating lease obligation			$ 0.9
Accrued operating lease obligation, noncurrent			$ 0.5