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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 year $ 576,030 $ 421,977 $ 377,506
Amount charged against operating revenue 3,994,924 3,362,081 2,825,827
Accounts receivable contractual adjustments and write-offs (net of recoveries) (3,946,058) (3,208,028) (2,781,356)
Balance at end of year $ 624,896 $ 576,030 $ 421,977