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Use of Estimates (Details) (USD $)
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2011
Use Of Estimates [Abstract]      
Allowances for contractual adjustments $ 218,884,000   $ 136,265,000
Allowances for accounts receivable 22,753,000   18,844,000
Bad debt expense included in other operating expenses $ 5,247,000 $ 4,050,000