Revenue Recognition - Summary of Impact of Adoption of Accounting Standards (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Royalty revenue	$ 11	$ 97
Contract revenue	2,177	471
Cost of contract revenue	1,635	403
Net loss	$ (7,132)	$ (5,949)
Net loss per share - basic and diluted	$ (0.09)	$ (0.09)
Costs and estimated earnings in excess of billings on uncompleted contracts	$ 258		$ 680
Other current assets	1,547		1,015
Deferred revenue - current			0
Deferred revenue - noncurrent			0
Accumulated deficit	$ (525,998)		(518,866)
Topic 606 | Previously reported
Royalty revenue		$ 535
Contract revenue		257
Cost of contract revenue		325
Net loss		$ (5,647)
Net loss per share - basic and diluted		$ (0.08)
Costs and estimated earnings in excess of billings on uncompleted contracts			680
Other current assets			945
Deferred revenue - current			999
Deferred revenue - noncurrent			4,151
Accumulated deficit			(524,086)
Topic 606 | Adjustment
Royalty revenue		$ (438)
Contract revenue		214
Cost of contract revenue		78
Net loss		$ (302)
Net loss per share - basic and diluted		$ (0.01)
Costs and estimated earnings in excess of billings on uncompleted contracts			0
Other current assets			70
Deferred revenue - current			(999)
Deferred revenue - noncurrent			(4,151)
Accumulated deficit			$ 5,220