Balance Sheet Components - Intangible Assets, net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets, net
Intangible assets, gross	$ 81,000	$ 81,000
Less: Accumulated amortization	(43,000)	(38,000)
Intangible assets, net	38,000	43,000
Amortization expense	5,000	5,000
Licenses
Intangible Assets, net
Intangible assets, gross	$ 81,000	$ 81,000