Accumulated Other Comprehensive (Loss) Income - Summary of Components of 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
Foreign currency transaction loss
Foreign currency transaction gain (loss)	$ 1,162	$ 1,260	$ 1,557	$ 1,491
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period			(93,194)
Total accumulated other comprehensive (loss) income, end of period	(90,540)		(90,540)
Accumulated other comprehensive (loss) income
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(91,530)	(98,212)	(93,194)	(99,005)
Gain (Loss) recognized in OCI, Net	58	(527)	810	(785)
Gain (Loss) reclassified from AOCI to income, Net	932	1,090	1,844	2,141
Total accumulated other comprehensive (loss) income, end of period	(90,540)	(97,649)	(90,540)	(97,649)
Changes in fair market value of hedges
Changes in AOCI, Gross
Gross, beginning of the period	1,308	(295)	116	(768)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(223)	(337)	819	(95)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(15)	229	135	460
Gross, ending balance	1,070	(403)	1,070	(403)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	(474)	110	(42)	289
Income tax (benefit), Gain (Loss) recognized in OCI	81	127	(297)	36
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	5	(86)	(49)	(174)
Income tax (benefit), ending of period	(388)	151	(388)	151
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	834	(185)	74	(479)
Gain (Loss) recognized in OCI, Net	(142)	(210)	522	(59)
Gain (Loss) reclassified from AOCI to income, Net	(10)	143	86	286
Total accumulated other comprehensive (loss) income, end of period	682	(252)	682	(252)
Changes in unrealized pension cost
Changes in AOCI, Gross
Gross, beginning of the period	(150,322)	(160,268)	(151,618)	(161,719)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	1,466	1,505	2,762	2,956
Gross, ending balance	(148,856)	(158,763)	(148,856)	(158,763)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	60,192	63,818	60,672	64,361
Income tax (benefit), Gain (Loss) recognized in OCI	0	0	0	0
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	(524)	(558)	(1,004)	(1,101)
Income tax (benefit), ending of period	59,668	63,260	59,668	63,260
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(90,130)	(96,450)	(90,946)	(97,358)
Gain (Loss) recognized in OCI, Net	0	0	0	0
Gain (Loss) reclassified from AOCI to income, Net	942	947	1,758	1,855
Total accumulated other comprehensive (loss) income, end of period	(89,188)	(95,503)	(89,188)	(95,503)
Cumulative translation adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,328)	(1,685)	(2,414)	(1,279)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	196	(310)	282	(716)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0	0
Gross, ending balance	(2,132)	(1,995)	(2,132)	(1,995)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	94	108	92	111
Income tax (benefit), Gain (Loss) recognized in OCI	4	(7)	6	(10)
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	0	0	0	0
Income tax (benefit), ending of period	98	101	98	101
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(2,234)	(1,577)	(2,322)	(1,168)
Gain (Loss) recognized in OCI, Net	200	(317)	288	(726)
Gain (Loss) reclassified from AOCI to income, Net	0	0	0	0
Total accumulated other comprehensive (loss) income, end of period	$ (2,034)	$ (1,894)	$ (2,034)	$ (1,894)