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Valuation and Qualifying Accounts (Detail) - Allowance for uncollectible Accounts - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of year $ 264,144 $ 242,674 $ 237,143
Amounts charged to income 463,030 437,100 381,337
Amounts written off 475,118 415,630 375,806
Balance at end of year $ 252,056 $ 264,144 $ 242,674