Changes in Initial Product Warranty Accrual and Expenses Under Initial and Extended Warranties (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in Standard Product Warranty Accrual
Initial warranty accrual, beginning balance	$ 2,188	$ 1,449	$ 1,096
Provision for estimated warranty cost	348	1,715	1,214
Warranty expenditures	(830)	(976)	(861)
Initial warranty accrual, ending balance	1,706	2,188	1,449
Less warranty accrual, long-term	773	843	519
Total warranty accrual, current portion	$ 933	$ 1,345	$ 930