CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 25,667	$ 13,824	$ 44,187	$ 15,366
Unrealized gain (loss) on defined benefit plan, net of tax	7,266	(2,238)	7,701	(1,382)
Unrealized gain (loss) on interest rate swap, net of tax	927	(647)	3,275	(120)
Unrealized foreign currency (loss) gain, net of tax	(24,985)	7,725	(9,130)	17,167
Comprehensive income	8,875	18,664	46,033	31,031
Less: Comprehensive income attributable to noncontrolling interest	(599)	(645)	(593)	(970)
Total comprehensive income attributable to common stockholders	$ 8,276	$ 18,019	$ 45,440	$ 30,061