Activity of Allowance for Sales Credit Memos (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 1,540	$ 1,997	$ 963
Provision for credit memos	8,005	2,164	5,374
Credit memos issued	(4,914)	(2,621)	(4,340)
Balance at end of year	$ 4,631	$ 1,540	$ 1,997