Recent Accounting Standards - Line Items Adjusted in Consolidated Statement of Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	$ 12,699	$ 18,184	$ 19,200	$ 43,694
Foreign currency translation adjustment	(607)	1,120	(3,059)	4,425
Comprehensive income	$ 12,092	19,304	$ 16,141	48,089
As Reported | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income		17,924		43,867
Foreign currency translation adjustment		1,060		4,090
Comprehensive income		18,984		47,927
Effect of the Adoption | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income		260		(173)
Foreign currency translation adjustment		60		335
Comprehensive income		$ 320		$ 162