CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 31,210	$ 14,778	$ 75,397	$ 30,144
Unrealized (loss) gain on defined benefit plan, net of tax	(493)	(1,135)	7,208	(2,517)
Unrealized gain on interest rate swap, net of tax	378	180	3,653	60
Unrealized foreign currency (loss) gain, net of tax	(9,848)	8,249	(18,978)	25,416
Comprehensive income	21,247	22,072	67,280	53,103
Less: Comprehensive income attributable to noncontrolling interest	(302)	(328)	(895)	(1,298)
Total comprehensive income attributable to common stockholders	$ 20,945	$ 21,744	$ 66,385	$ 51,805