Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Raw materials	$ 25	$ 180
Work in process	773	1,301
Finished goods	1,547	1,731
Total inventories	2,345	3,212
Inventory write offs	$ 2,400	$ 1,000	$ 800