Summary of Significant Accounting Policies - Reconciliation of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 4,447	$ 5,728
Provision for credit losses	2,257	2,335	$ 2,398
Write-off of uncollectible amounts, net of recoveries	(1,094)	(3,616)	(2,315)
Ending balance	$ 5,610	$ 4,447	$ 5,728