Balance Sheet Components - Intellectual Property Prepaid Royalties and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intellectual Property Prepaid Royalties
Amortization for license agreements	$ 1,200	$ 1,200	$ 1,300
Future amortization expense, prepaid royalties
2018	1,083
2019	675
2020	502
2021	502
2022	493
Thereafter	2,365
Total	$ 5,620