Allowance for Doubtful Accounts (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 4,544	$ 4,157	$ 4,040
Accounts written off	(25,178)	(23,601)	(20,352)
Bad debt expense	25,402	23,988	20,469
Ending Balance	$ 4,768	$ 4,544	$ 4,157