Accumulated Other Comprehensive (Loss) Income - Summary of Components of Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Foreign currency transaction loss
Foreign currency transaction gain (loss)	$ 960	$ 165	$ 2,517	$ 1,656
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	(89,485)		(89,485)
Accumulated other comprehensive (loss) income
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(90,540)	(97,649)	(93,194)	(99,005)
Gain (Loss) recognized in OCI, Net	187	(565)	997	(1,354)
Gain (Loss) reclassified from AOCI to income, Net	868	1,036	2,712	3,181
Total accumulated other comprehensive (loss) income, end of period	(89,485)	(97,178)	(89,485)	(97,178)
Changes in fair market value of hedges
Changes in AOCI, Gross
Gross, beginning of the period	1,070	(403)	116	(768)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	37	(643)	856	(742)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(108)	221	27	685
Gross, ending balance	999	(825)	999	(825)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	(388)	151	(42)	289
Income tax (benefit), Gain (Loss) recognized in OCI	(14)	242	(311)	278
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	40	(83)	(9)	(257)
Income tax (benefit), ending of period	(362)	310	(362)	310
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	682	(252)	74	(479)
Gain (Loss) recognized in OCI, Net	23	(401)	545	(464)
Gain (Loss) reclassified from AOCI to income, Net	(68)	138	18	428
Total accumulated other comprehensive (loss) income, end of period	637	(515)	637	(515)
Changes in unrealized pension cost
Changes in AOCI, Gross
Gross, beginning of the period	(148,856)	(158,763)	(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	1,458	1,437	4,220	4,393
Gross, ending balance	(147,398)	(157,326)	(147,398)	(157,326)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	59,668	63,260	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	(522)	(539)	(1,526)	(1,640)
Income tax (benefit), ending of period	59,146	62,721	59,146	62,721
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(89,188)	(95,503)	(90,946)	(97,358)
Gain (Loss) recognized in OCI, Net	0	0	0	0
Gain (Loss) reclassified from AOCI to income, Net	936	898	2,694	2,753
Total accumulated other comprehensive (loss) income, end of period	(88,252)	(94,605)	(88,252)	(94,605)
Cumulative translation adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,132)	(1,995)	(2,414)	(1,279)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	161	(161)	443	(877)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0	0
Gross, ending balance	(1,971)	(2,156)	(1,971)	(2,156)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	98	101	92	111
Income tax (benefit), Gain (Loss) recognized in OCI	3	(3)	9	(13)
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	0	0	0	0
Income tax (benefit), ending of period	101	98	101	98
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(2,034)	(1,894)	(2,322)	(1,168)
Gain (Loss) recognized in OCI, Net	164	(164)	452	(890)
Gain (Loss) reclassified from AOCI to income, Net	0	0	0	0
Total accumulated other comprehensive (loss) income, end of period	$ (1,870)	$ (2,058)	$ (1,870)	$ (2,058)