Allowance for Doubtful Accounts Receivable and Sales Returns (Activity in Allowance for Doubtful Accounts Receivable and Sales Returns) (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]
Beginning Balance	$ 937	$ 802
Ending Balance	560	937	$ 802
Allowance for Doubtful Accounts Receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	725	633	765
Addition (reduction) to allowance	(224)	(14)	36
Amounts written off	0	0	(152)
Effects of foreign currency translation	(26)	106	(16)
Ending Balance	475	725	633
Allowance for Sales Returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	212	169	158
Addition (reduction) to allowance	(126)	55	15
Amounts written off	0	(11)	(3)
Effects of foreign currency translation	(1)	(1)	(1)
Ending Balance	$ 85	$ 212	$ 169