Accounts Receivable - Summary of Activity in Allowances for Doubtful Accounts, Returns and Discounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Balance at Beginning of Period	$ 4,631	$ 4,831	$ 4,340
Charges to Revenue	1,949	4,030	1,488
Charges (Credits) to Expense	572	881	1,100
Additions to (Deductions from) Reserves	(3,655)	(5,111)	(2,097)
Balance at End of Period	$ 3,497	$ 4,631	$ 4,831