Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Related to Accounts Receivable (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts beginning of year		$ 46,031	$ 32,506	$ 21,903
Provision for bad debts	[1]	64,377	44,857	35,885
Write-offs		(50,445)	(31,332)	(25,282)
Allowance for doubtful accounts end of year		$ 59,963	$ 46,031	$ 32,506

[1] Reflects the impact of the Company's adoption of Accounting Standards Update 2016-18, Statement of Cash Flows (Topic 230), which was adopted by the Company on January 1, 2018 and applied retrospectively to results for 2017. The adoption of Topic 230 resulted in the statement of cash flows presenting the changes in the total of cash, cash equivalents and restricted cash. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash in the statement of cash flows.