Balance Sheet Components - Schedule of Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2008
Intangible assets, net
Acquired intangible assets				$ 910,000
Amortization of intangible assets		$ (910,000)
Amortization expense	$ 0	$ 132,000	$ 150,000