CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 13,824	$ 6,396	$ 15,366	$ 4,911
Unrealized (loss) on defined benefit plan, net of tax	(2,238)	(5,087)	(1,382)	(5,161)
Unrealized (loss) on interest rate swap, net of tax	(647)		(120)
Unrealized foreign currency gain (loss), net of tax	7,725	(10,653)	17,167	(7,775)
Comprehensive income (loss)	18,664	(9,344)	31,031	(8,025)
Less: Comprehensive income attributable to noncontrolling interest	(645)	(644)	(970)	(892)
Total comprehensive income (loss) attributable to common stockholders	$ 18,019	$ (9,988)	$ 30,061	$ (8,917)