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Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Related to Accounts Receivable (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Accounting Policies [Abstract]      
Allowance for doubtful accounts beginning of year $ 23,842 $ 22,416 $ 19,463
Provision for bad debts 24,629 24,412 18,867
Write-offs (26,568) (22,986) (15,914)
Allowance for doubtful accounts end of year $ 21,903 $ 23,842 $ 22,416