Shareholders' Equity - Components of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 263,477	$ 263,477	$ 290,311	$ 299,627
Other comprehensive income (loss)		8,382	(2,830)
Income taxes		(1,475)	791
Other expense, net	5,600	5,585	2,727
Income taxes		29,100	15,527	10,849
Ending Balance		296,608	263,477	290,311
Reclassification Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other expense, net		5,585	2,727
Income taxes		(2,125)	(1,036)
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(5,115)	(5,115)	(4,389)
Other comprehensive income (loss)		4,552	(726)
Ending Balance		(563)	(5,115)	(4,389)
Derivatives [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			228
Other comprehensive income (loss)			(360)
Income taxes			132
Ending Balance				228
Debt Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(1,465)	(1,465)	(2,071)
Other comprehensive income (loss)		3,830	(1,744)
Income taxes		(1,475)	659
Ending Balance		4,350	(1,465)	(2,071)
Debt Securities [Member] | Reclassification Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other expense, net		5,585	2,727
Income taxes		(2,125)	(1,036)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ (6,580)	(6,580)	(6,232)	(382)
Ending Balance		$ 3,787	$ (6,580)	$ (6,232)