CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 105,406	$ 266	$ 18,477
Unrealized gain (loss) on defined benefit plan, net of tax	3,440	(4,897)	(7,777)
Unrealized gain on interest rate swap, net of tax	737	1,018	1,506
Unrealized foreign currency (gain) loss, net of tax	(22,543)	33,065	(21,979)
Comprehensive income (loss)	87,040	29,452	(9,773)
Less: Comprehensive income attributable to noncontrolling interest	(1,385)	(2,071)	(2,542)
Total comprehensive income (loss) attributable to common stockholders	$ 85,655	$ 27,381	$ (12,315)