Summary of Changes in Reserve for Allowance for Doubtful Accounts, Sales Returns and Allowances (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of fiscal year	$ 15,253	$ 9,975	$ 6,392
(Credit) charges to expenses	(566)	1,386	2,997
(Write-offs) recoveries, net	(4,457)	3,892	586
Balance at end of fiscal year	$ 10,230	$ 15,253	$ 9,975