Activity of Allowance for Sales Credit Memos (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 895	$ 1,027	$ 540
Provision for credit memos	1,773	2,877	3,050
Credit memos issued	(1,705)	(3,009)	(2,563)
Balance at end of year	$ 963	$ 895	$ 1,027