Balance Sheet Components - Property and Equipment Net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and Equipment
Total property and equipment	$ 2,473,000	$ 1,875,000
Less: accumulated depreciation and amortization	(1,594,000)	(1,313,000)
Property and equipment, net	879,000	562,000
Property and equipment income statement disclosure
Depreciation expense	406,000	317,000	$ 247,000
Laboratory equipment
Property and Equipment
Total property and equipment	2,177,000	1,650,000
Furniture and computer equipment
Property and Equipment
Total property and equipment	270,000	163,000
Leasehold improvements
Property and Equipment
Total property and equipment	26,000	62,000
Australia
Property and Equipment
Property and equipment, net	$ 1,200	$ 8,000