Revenue Recognition - Summary of Impact of Adoption of Accounting Standards (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Product revenue	$ 0	$ 2,253	$ 0	$ 2,298
Royalty revenue	10,000	77	10,011	280
Contract revenue	1,572	3,095	5,763	4,754
Cost of product revenue	1,434	3,178	1,998	3,572
Cost of contract revenue	1,211	2,525	4,201	3,740
Net loss	289	(5,762)	(15,302)	(17,367)
Costs and estimated earnings in excess of billings on uncompleted contracts	1,080		1,080		$ 680
Other current assets	893		893		1,015
Billings on uncompleted contracts	1		1		5
Deferred revenue - current					0
Deferred revenue - noncurrent					0
Accumulated deficit	$ (534,168)		$ (534,168)		(518,866)
Topic 606 | Previously reported
Product revenue		2,298		2,298
Royalty revenue		359		1,240
Contract revenue		3,429		4,793
Cost of product revenue		3,224		3,572
Cost of contract revenue		2,619		3,754
Net loss		$ (5,241)		$ (16,382)
Net loss per share - basic and diluted		$ (0.07)		$ (0.23)
Costs and estimated earnings in excess of billings on uncompleted contracts					680
Other current assets					945
Billings on uncompleted contracts					5
Deferred revenue - current					999
Deferred revenue - noncurrent					4,151
Accumulated deficit					(524,086)
Topic 606 | Adjustment
Product revenue		$ (45)		$ 0
Royalty revenue		(282)		(960)
Contract revenue		(334)		(39)
Cost of product revenue		(46)		0
Cost of contract revenue		(94)		(14)
Net loss		$ (521)		$ (985)
Net loss per share - basic and diluted		$ (0.01)		$ (0.02)
Costs and estimated earnings in excess of billings on uncompleted contracts					0
Other current assets					70
Billings on uncompleted contracts					0
Deferred revenue - current					(999)
Deferred revenue - noncurrent					(4,151)
Accumulated deficit					$ 5,220