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, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 802	$ 923
Ending Balance	937	802	$ 923
Allowance for Doubtful Accounts Receivable
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	633	765	1,288
Addition (reduction) to allowance	(14)	36	(355)
Amounts written off	0	(152)	(77)
Effects of foreign currency translation	106	(16)	(91)
Ending Balance	725	633	765
Allowance for Sales Returns
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	169	158	354
Addition (reduction) to allowance	55	15	(186)
Amounts written off	(11)	(3)	(9)
Effects of foreign currency translation	(1)	(1)	(1)
Ending Balance	$ 212	$ 169	$ 158