Schedule II -Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 1,568
Balance at End of Period	1,646	$ 1,568
Reserve for Uncollectible Accounts Receivable and Sales Return [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1,568	873	$ 736
Charged to Costs and Expenses	464	724	216
Deductions	(343)	(116)	(64)
Other	(43)	87	(15)
Balance at End of Period	1,646	1,568	873
Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	5,309	4,116	3,259
Charged to Costs and Expenses	803	1,193	857
Deductions	0	0	0
Other	0	0	0
Balance at End of Period	$ 6,112	$ 5,309	$ 4,116