Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			$ 561,212
Total amount reclassified from Accumulated other comprehensive loss, net of tax	$ 0	$ 2,022	0	$ 4,125
Other comprehensive income (loss)	16,280	(11,140)	29,008	6,803
Balance at end of period	601,596		601,596
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	(116,084)	(117,497)	(118,068)	(119,389)
Tax benefit	(935)	(1,042)	(2,043)	(2,086)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	2,157	1,894	4,141	3,786
Balance at end of period	(113,927)	(115,603)	(113,927)	(115,603)
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	(109)	(90)	(218)	(180)
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	3,201	3,026	6,402	6,052
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	(100,808)	(73,083)	(112,178)	(88,810)
Reclassification into earnings	0	1,252	0	3,355
Other comprehensive income (loss)	14,960	(15,042)	26,330	(1,418)
Balance at end of period	(85,848)	(86,873)	(85,848)	(86,873)
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	(2,590)	(3,292)	(1,964)	(3,616)
Reclassification into earnings	0		0	770
Other comprehensive income (loss)	(837)	(14)	(1,463)	310
Balance at end of period	$ (3,427)	$ (2,536)	$ (3,427)	$ (2,536)