Summary of Significant Accounting Policies - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 141,189	$ 150,036	$ 127,302
Foreign currency translation before reclassification			(2,764)
Foreign currency translation	(3,257)	5,593	(2,764)
Reclassification of stranded tax effects from tax reform	(26)
Unrealized (gain) loss on investments before reclassification, net of tax	12	(32)	17
Reclassification adjustment for net losses realized in net income, net of tax	129
Ending Balance	151,600	141,189	150,036
Net Unrealized Gain (Loss) on Marketable Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(115)	(83)	(100)
Reclassification of stranded tax effects from tax reform	(26)
Unrealized (gain) loss on investments before reclassification, net of tax	12	(32)	17
Reclassification adjustment for net losses realized in net income, net of tax	129
Ending Balance		(115)	(83)
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,897)	(7,490)	(4,726)
Foreign currency translation before reclassification			(2,764)
Foreign currency translation	(3,257)	5,593
Ending Balance	(5,154)	(1,897)	(7,490)
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2,012)	(7,573)	(4,826)
Foreign currency translation	(3,257)	5,593	(2,764)
Ending Balance	$ (5,154)	$ (2,012)	$ (7,573)