Accumulated Other Comprehensive Loss - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (2,012)
Reclassification of stranded tax effects from tax reform	(26)
Foreign currency translation	1,703	$ 790
Unrealized gain (loss) on investments, net of tax	(115)	17
Ending Balance	(450)
Beginning Balance	141,189
Ending Balance	141,295
Net Unrealized Loss on Marketable Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(115)	(83)
Reclassification of stranded tax effects from tax reform	(26)
Unrealized gain (loss) on investments, net of tax	(115)	17
Ending Balance	(256)	(66)
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,897)	(7,490)
Foreign currency translation	1,703	790
Ending Balance	(194)	(6,700)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2,012)	(7,573)
Ending Balance	$ (450)	$ (6,766)