Summary of Significant Accounting Policies - Allowance for Doubtful Accounts and Other Accounts Receivable Allowances (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance For Doubtful Accounts Receivable Rollforward
Allowance, balance at the beginning	$ 10,116	$ 9,755	$ 8,046
Provision charged to income	764	45	1,917
Accounts written off, net of recoveries	(1,226)	316	(208)
Allowance, balance at ending	$ 9,654	$ 10,116	$ 9,755