Significant Accounting Policies - Summary of Activity in Product Warranty Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Reserve at beginning of year	$ 10,634	$ 12,339	$ 14,005
Additions	10,310	8,349	9,122
Payments	(8,851)	(10,054)	(10,788)
Reserve at end of year	$ 12,093	$ 10,634	$ 12,339