Segments and Geographic Information - Schedule of Other Information by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Product revenues									$ 32,688	$ 27,211	$ 22,891
Service revenues									17,291	13,065	11,651
Royalties										14,297	3,745
Total revenues	$ 11,790	$ 12,986	$ 13,956	$ 11,247	$ 20,930	$ 11,556	$ 11,610	$ 10,477	49,979	54,573	38,287
Cost of product revenues									19,013	15,595	13,053
Cost of service revenues									9,948	8,698	8,361
Total cost of revenues									28,961	24,293	21,414
Gross profit	4,754	5,267	6,306	4,691	15,159	5,851	5,143	4,127	21,018	30,280	16,873
Total operating expenses	$ 5,271	$ 6,802	$ 6,662	$ 6,146	$ 6,042	$ 5,674	$ 7,420	$ 5,865	24,881	25,001	18,746
Total non-operating income									1,617	763	382
(Loss) income before income taxes									(2,246)	6,042	(1,491)
Product [Member]
Revenues
Product revenues									32,688	27,211	22,891
Royalties										14,297	3,745
Total revenues									32,688	41,508	26,636
Cost of product revenues									19,013	15,595	13,053
Total cost of revenues									19,013	15,595	13,053
Gross profit									13,675	25,913	13,583
Service [Member]
Revenues
Service revenues									17,291	13,065	11,651
Total revenues									17,291	13,065	11,651
Cost of service revenues									9,948	8,698	8,361
Total cost of revenues									9,948	8,698	8,361
Gross profit									$ 7,343	$ 4,367	$ 3,290