Changes in Initial Product Warranty Accrual and Expenses Under Initial and Extended Warranties (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Movement in Standard Product Warranty Accrual
Initial warranty accrual, beginning balance	$ 1,706	$ 2,188
Provision for estimated warranty cost	(23)	61
Warranty expenditures	(223)	(189)
Initial warranty accrual, ending balance	1,460	2,060
Less warranty accrual, long-term	487	973	$ 773
Total warranty accrual, current portion	$ 973	$ 1,087	$ 933