Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 34,669	$ 98,044	$ 27,835
Unrealized gain (loss) on investment	(26)	(33)	91
Ending balance	90,722	34,669	98,044
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,304)	(223)	83
Foreign currency translation adjustment	1,184	(1,048)	(397)
Unrealized gain (loss) on investment	(26)	(33)	91
Ending balance	$ (146)	$ (1,304)	$ (223)