Revenue Recognition - Impact to Financial Statements (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenues:
Total revenues	$ 16,946	$ 9,984	$ 44,526	$ 28,301
Costs and operating expenses:
Cost of product revenue	3,791	3,976	10,228	10,768
Research and development	7,917	8,055	22,464	20,242
Selling, general and administrative	7,344	7,989	22,485	21,141
Total costs and operating expenses	19,052	20,020	55,177	52,151
Loss from operations	(2,106)	(10,036)	(10,651)	(23,850)
Interest income	199	28	444	96
Other expenses	(80)	(68)	(221)	(80)
Loss before income taxes	(1,987)	(10,076)	(10,428)	(23,834)
Provision for (benefit from) income taxes	1	150	(11)	132
Net loss	$ (1,988)	$ (10,226)	$ (10,417)	$ (23,966)
Net loss per share, basic and diluted (usd per share)	$ (0.04)	$ (0.21)	$ (0.20)	$ (0.53)
Weighted average common stock shares used in computing net loss per share, basic and diluted (shares)	53,597	48,147	51,609	45,568
Assets
Accounts Receivable	$ 9,308		$ 9,308		$ 11,800
Contract assets	1,868		1,868		0
Inventories, net	830		830		1,036
Other non-current assets	304		304		302
Liabilities
Other accrued liabilities	5,933		5,933		4,362
Deferred revenue	4,253		4,253		12,292
Deferred revenue - non-current	4,431		4,431		1,501
Stockholders' equity:
Accumulated deficit	(330,014)		(330,014)		(315,065)
Balances without adoption of Topic 606 [Member]
Revenues:
Total revenues	15,986		38,126
Costs and operating expenses:
Cost of product revenue	3,350		8,432
Research and development	7,821		22,288
Selling, general and administrative	7,344		22,485
Total costs and operating expenses	18,515		53,205
Loss from operations	(2,529)		(15,079)
Interest income	199		444
Other expenses	(80)		(221)
Loss before income taxes	(2,410)		(14,856)
Provision for (benefit from) income taxes	1		(11)
Net loss	$ (2,411)		$ (14,845)
Net loss per share, basic and diluted (usd per share)	$ (0.04)		$ (0.29)
Weighted average common stock shares used in computing net loss per share, basic and diluted (shares)	53,597		51,609
Assets
Accounts Receivable	$ 7,448		$ 7,448
Contract assets	0		0
Inventories, net	946		946
Other non-current assets	241		241
Liabilities
Other accrued liabilities	4,017		4,017
Deferred revenue	3,598		3,598
Deferred revenue - non-current	3,697		3,697
Stockholders' equity:
Accumulated deficit	(330,383)		(330,383)
Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Revenues:
Total revenues	(960)		(6,400)
Costs and operating expenses:
Cost of product revenue	(441)		(1,796)
Research and development	(96)		(176)
Selling, general and administrative	0		0
Total costs and operating expenses	(537)		(1,972)
Loss from operations	(423)		(4,428)
Interest income	0		0
Other expenses	0		0
Loss before income taxes	(423)		(4,428)
Provision for (benefit from) income taxes	0		0
Net loss	$ (423)		$ (4,428)
Net loss per share, basic and diluted (usd per share)	$ 0.00		$ (0.09)
Assets
Accounts Receivable	$ (1,860)		$ (1,860)
Contract assets	(1,868)		(1,868)
Inventories, net	116		116
Other non-current assets	(63)		(63)
Liabilities
Other accrued liabilities	(1,916)		(1,916)
Deferred revenue	(655)		(655)
Deferred revenue - non-current	(734)		(734)
Stockholders' equity:
Accumulated deficit	(369)		(369)		$ (4,100)
Product Sales [Member]
Revenues:
Total revenues	8,405	$ 6,948	18,291	$ 19,134
Product Sales [Member] | Balances without adoption of Topic 606 [Member]
Revenues:
Total revenues	5,470		12,387
Product Sales [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Revenues:
Total revenues	(2,935)		(5,904)
Research and Development Revenue [Member]
Revenues:
Total revenues	8,541	$ 3,036	26,235	$ 9,167
Research and Development Revenue [Member] | Balances without adoption of Topic 606 [Member]
Revenues:
Total revenues	10,516		25,739
Research and Development Revenue [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Revenues:
Total revenues	$ 1,975		$ (496)