Condensed Statements of Comprehensive Loss - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Total revenues	$ 3,985,000	$ 3,413,000	$ 8,116,000	$ 6,901,000
Operating expenses:
Cost of product revenues	$ 879,000	$ 1,084,000	$ 2,015,000	$ 2,258,000
Type of cost, good or service [extensible list]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 6,598,000	$ 6,120,000	$ 12,849,000	$ 13,072,000
Selling, general and administrative	3,278,000	2,816,000	6,732,000	6,010,000
Total operating expenses	10,755,000	10,020,000	21,596,000	21,340,000
Loss from operations	(6,770,000)	(6,607,000)	(13,480,000)	(14,439,000)
Other income (expense):
Interest and other income	177,000	240,000	386,000	398,000
Interest expense	(634,000)	(644,000)	(1,263,000)	(1,267,000)
Net other expense	(457,000)	(404,000)	(877,000)	(869,000)
Net loss	(7,227,000)	(7,011,000)	(14,357,000)	(15,308,000)
Net change in unrealized loss on available-for-sale securities, net of reclassification adjustments and taxes	(3,000)	1,000	(7,000)	1,000
Total comprehensive loss	$ (7,230,000)	$ (7,010,000)	$ (14,364,000)	$ (15,307,000)
Net loss per share
Basic	$ (0.04)	$ (0.04)	$ (0.09)	$ (0.10)
Diluted	$ (0.04)	$ (0.04)	$ (0.09)	$ (0.10)
Weighted-average shares used in computing net loss per share
Basic	164,359	161,621	163,219	157,612
Diluted	164,359	161,621	163,219	157,612
Collaborative Research and Development and Other Revenue [Member]
Total revenues	$ 1,639,000	$ 645,000	$ 3,139,000	$ 1,741,000
Product Revenue, Net [Member]
Total revenues	$ 2,346,000	$ 2,768,000	$ 4,977,000	$ 5,160,000