Allowance for Doubtful Accounts (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 4,768	$ 4,544	$ 4,157
Accounts written off	(30,609)	(25,178)	(23,601)
Bad debt expense	31,842	25,402	23,988
Ending Balance	$ 6,001	$ 4,768	$ 4,544