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Accounts Receivable - Allowance for Doubtful Accounts Related to Accounts Receivable (Detail) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Receivables [Abstract]    
Allowance for doubtful accounts beginning of period $ 19,463 $ 15,315
Provision for bad debts 9,199 10,953
Write-offs (8,422) (8,309)
Allowance for doubtful accounts end of period $ 20,240 $ 17,959