CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 11,534	$ 3,635	$ 16,445	$ 31,269
Foreign currency translation adjustment	1,546	(11,954)	(6,246)	(13,205)
Unrealized (loss) gain on defined benefit plan, net of tax	(9,571)	1,852	(14,732)	4,487
Unrealized foreign currency loss, net of tax	(359)	(343)	(342)	(444)
Comprehensive income (loss)	3,150	(6,810)	(4,875)	22,107
Less: Comprehensive income attributable to noncontrolling interest	(886)	(798)	(1,778)	(2,222)
Total comprehensive income (loss) attributable to common stockholders	$ 2,264	$ (7,608)	$ (6,653)	$ 19,885