Valuation and Qualifying Accounts (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 253,405	$ 248,622	$ 168,876
Charges to costs and expenses	726,671	613,619	546,909
Acquisition of business	5,632		56,596
Write-off of uncollectible accounts	(674,321)	(608,836)	(523,759)
Balance at end of period	$ 311,387	$ 253,405	$ 248,622