Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			$ 602,578
Total amount reclassified from Accumulated other comprehensive loss, net of tax	$ 0	$ 0	(774)	$ 0
Other comprehensive income (loss)	(2,104)	12,201	(11,970)	41,209
Balance at end of period	659,706		659,706
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(92,560)	(113,927)	(97,948)	(118,068)
Tax benefit	(886)	(1,009)	(2,566)	(3,052)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	2,651	2,180	8,039	6,321
Balance at end of period	(89,909)	(111,747)	(89,909)	(111,747)
Accumulated Defined Benefit Plans Adjustment Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	0	0
Tax benefit	0	0	0	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	0	0	0
Balance at end of period	0	0	0	0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Amounts reclassified from Accumulated other comprehensive loss	(105)	(10)	(319)	(228)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Amounts reclassified from Accumulated other comprehensive loss	0	0	0	0
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Amounts reclassified from Accumulated other comprehensive loss	3,642	3,199	10,924	9,601
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Amounts reclassified from Accumulated other comprehensive loss	0	0	0	0
Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(88,965)	(85,848)	(73,814)	(112,178)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent			(774)	0
Other comprehensive income (loss)	(4,561)	5,892	(18,938)	32,222
Balance at end of period	(93,526)	(79,956)	(93,526)	(79,956)
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	698	(3,427)	801	(1,964)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent			0	0
Other comprehensive income (loss)	(194)	4,129	(297)	2,666
Balance at end of period	$ 504	$ 702	$ 504	$ 702