Accumulated Other Comprehensive Loss - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 149,686	$ 140,111	$ 151,600	$ 141,189
Reclassification of stranded tax effects from tax reform				(26)
Foreign currency translation	(1,614)	(602)	(1,450)	(2,293)
Unrealized gain on investments, net of tax		65		12
Ending Balance	147,652	146,830	147,652	146,830
Net Unrealized Loss on Marketable Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(194)		(115)
Reclassification of stranded tax effects from tax reform				(26)
Unrealized gain on investments, net of tax		65		12
Ending Balance		(129)		(129)
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,990)	(3,588)	(5,154)	(1,897)
Foreign currency translation	(1,614)	(602)	(1,450)	(2,293)
Ending Balance	(6,604)	(4,190)	(6,604)	(4,190)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,990)	(3,782)	(5,154)	(2,012)
Foreign currency translation	(1,614)	(602)	(1,450)	(2,293)
Ending Balance	$ (6,604)	$ (4,319)	$ (6,604)	$ (4,319)