Accumulated Other Comprehensive Loss - Components of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 296,608
Other comprehensive income	697
Income taxes	5,373	$ 3,924
Ending Balance	313,174
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(563)
Other comprehensive income	697
Ending Balance	134
Debt Security [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	4,350
Ending Balance	4,350
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	3,787
Ending Balance	$ 4,484