Revenue Recognition - Impact to Financial Statements (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenues:
Total revenues	$ 60,594	$ 50,024	$ 48,837
Cumulative effect of change in accounting principles	(4,059)
Costs and operating expenses:
Cost of product revenue	12,620	14,327	9,753
Research and development	29,978	29,659	22,229
Selling, general and administrative	29,291	29,008	25,419
Total costs and operating expenses	71,889	72,994	57,401
Loss from operations	(11,295)	(22,970)	(8,564)
Interest income	671	147	60
Other expenses, net	(291)	(92)	(94)
Loss before income taxes	(10,915)	(22,915)	(8,598)
Provision for (benefit from) income taxes	(37)	81	(40)
Net loss	$ (10,878)	$ (22,996)	$ (8,558)
Net loss per share, basic and diluted (usd per share)	$ (0.21)	$ (0.50)	$ (0.21)
Weighted average common stock shares used in computing net loss per share, basic and diluted (shares)	52,205	46,228	40,629
Assets
Accounts receivable	$ 11,551	$ 11,447
Unbilled receivables, current	1,916	353		$ 0
Contract assets	35	0		0
Inventories	589	1,036
Unbilled receivables, non-current	786			$ 0
Other non-current assets	265
Liabilities
Other accrued liabilities	4,855	4,362
Deferred revenue - current	4,936	12,292
Deferred revenue - non-current	3,352	1,501
Stockholders’ equity:
Accumulated deficit	(330,474)	(315,065)
Product Sales
Revenues:
Total revenues	25,590	26,685	$ 15,321
Research and Development Revenues
Revenues:
Total revenues	35,004	$ 23,339
Balances without adoption of Topic 606
Revenues:
Total revenues	55,563
Costs and operating expenses:
Cost of product revenue	12,335
Research and development	29,782
Selling, general and administrative	29,291
Total costs and operating expenses	71,408
Loss from operations	(15,845)
Interest income	671
Other expenses, net	(291)
Loss before income taxes	(15,465)
Provision for (benefit from) income taxes	(37)
Net loss	$ (15,428)
Net loss per share, basic and diluted (usd per share)	$ (0.30)
Weighted average common stock shares used in computing net loss per share, basic and diluted (shares)	52,205
Assets
Accounts receivable	$ 10,298
Unbilled receivables, current	0
Contract assets	0
Inventories	590
Unbilled receivables, non-current	0
Other non-current assets	223
Liabilities
Other accrued liabilities	4,335
Deferred revenue - current	3,362
Deferred revenue - non-current	1,907
Stockholders’ equity:
Accumulated deficit	(330,966)
Balances without adoption of Topic 606 | Product Sales
Revenues:
Total revenues	22,168
Balances without adoption of Topic 606 | Research and Development Revenues
Revenues:
Total revenues	33,395
Accounting Standards Update 2014-09 | Adjustments
Revenues:
Total revenues	(5,031)
Costs and operating expenses:
Cost of product revenue	(285)
Research and development	(196)
Selling, general and administrative	0
Total costs and operating expenses	(481)
Loss from operations	(4,550)
Interest income	0
Other expenses, net	0
Loss before income taxes	(4,550)
Provision for (benefit from) income taxes	0
Net loss	$ (4,550)
Net loss per share, basic and diluted (usd per share)	$ (0.09)
Assets
Accounts receivable	$ (1,253)
Unbilled receivables, current	(1,916)
Contract assets	(35)
Inventories	1
Unbilled receivables, non-current	(786)
Other non-current assets	(42)
Liabilities
Other accrued liabilities	(520)
Deferred revenue - current	(1,574)
Deferred revenue - non-current	(1,445)
Stockholders’ equity:
Accumulated deficit	(492)
Accounting Standards Update 2014-09 | Adjustments | Product Sales
Revenues:
Total revenues	(3,422)
Accounting Standards Update 2014-09 | Adjustments | Research and Development Revenues
Revenues:
Total revenues	$ (1,609)