Revenue by Geographical Location (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue, Major Customer [Line Items]
Product revenue	$ 10,125	$ 10,175	$ 9,251	$ 7,632	$ 9,656	$ 8,045	$ 8,830	$ 7,692	$ 37,183	$ 34,223	$ 36,416
Government contracts revenue	$ 1,831	$ 261							2,092
Total revenue									39,275	34,223	36,416
BELGIUM
Revenue, Major Customer [Line Items]
Product revenue									6,392	5,728	4,456
UNITED STATES
Revenue, Major Customer [Line Items]
Product revenue									4,480	563	350
Government contracts revenue									2,092
KUWAIT
Revenue, Major Customer [Line Items]
Product revenue									4,415	1,959	2,557
FRANCE
Revenue, Major Customer [Line Items]
Product revenue									3,485	7,732	9,184
SPAIN
Revenue, Major Customer [Line Items]
Product revenue									3,360	4,070	2,776
SWITZERLAND
Revenue, Major Customer [Line Items]
Product revenue									3,324	2,938	3,784
CIS
Revenue, Major Customer [Line Items]
Product revenue									2,859	3,361	6,636
Other Countries
Revenue, Major Customer [Line Items]
Product revenue									$ 8,868	$ 7,872	$ 6,673