Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Related to Accounts Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts beginning of year	$ 21,903	$ 23,842	$ 22,416
Provision for bad debts	35,885	24,629	24,412
Allowance for Doubtful Accounts Receivable, Write-offs	25,282	26,568	22,986
Allowance for doubtful accounts end of year	$ 32,506	$ 21,903	$ 23,842