Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation	$ 1.9	$ 1.6	$ 3.5	$ 3.7
Capitalized costs	0.7	1.1	1.6	2.1
Amortization expense	0.4	$ 0.0	0.4	$ 0.6
Unamortized costs	$ 5.6		$ 5.6		$ 4.4