Accumulated Other Comprehensive Loss - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ (2,012)
Reclassification of stranded tax effects from tax reform			(26)
Foreign currency translation	$ (602)	$ 1,601	(2,293)	$ 4,905
Unrealized gain on investments, net of tax	65	23	12	47
Ending Balance	(4,319)		(4,319)
Beginning Balance			141,189
Ending Balance	146,830		146,830
Net Unrealized Loss on Marketable Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(194)	(59)	(115)	(83)
Reclassification of stranded tax effects from tax reform			(26)
Unrealized gain on investments, net of tax	65	23	12	47
Ending Balance	(129)	(36)	(129)	(36)
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3,588)	(4,186)	(1,897)	(7,490)
Foreign currency translation	(602)	1,601	(2,293)	4,905
Ending Balance	(4,190)	(2,585)	(4,190)	(2,585)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3,782)	(4,245)	(2,012)	(7,573)
Ending Balance	$ (4,319)	$ (2,621)	$ (4,319)	$ (2,621)