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Valuation And Qualifying Accounts (Details) (Allowance For Doubtful Accounts [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Allowance For Doubtful Accounts [Member]
     
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance beginning of period $ 7,935 $ 6,175 $ 4,776
Additions charged to expense 24,877 24,216 20,808
Deductions (25,533) (22,456) (19,409)
Balance end of period $ 7,279 $ 7,935 $ 6,175
Bad debt expense as a % of revenue 4.00% 3.80% 4.10%