Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 410,374	$ 398,797	$ 324,648
Charges to costs and expenses (income)	869,077	741,578	741,273
Write-off of uncollectible accounts	(799,162)	(730,001)	(667,124)
Balance at end of period	480,289	410,374	398,797
Valuation Allowance for Deferred Tax Assets
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	56,333	52,567	52,764
Charges to costs and expenses (income)	13,894	3,766	(197)
Balance at end of period	$ 70,227	$ 56,333	$ 52,567