Summary of Opening and Closing Balances of Contract Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Revenue Recognition [Abstract]
Undelivered elements (training and product and support services; installation for 2017)	$ 583	$ 980
Extended warranty contracts	1,592	1,634
Deferred royalties	20	22
Total deferred revenue	2,195	2,636
Less long-term amounts:
Deferred royalties	8	11
Total deferred revenue - long-term	8	11
Total deferred revenue - current	$ 2,187	$ 2,625