Accumulated Other Comprehensive (Loss) Income - Summary of Components of Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Foreign currency transaction loss
Foreign currency transaction gain (loss)	$ 2,194	$ (1,162)	$ 918	$ (1,557)
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period			(78,960)
Total accumulated other comprehensive (loss) income, end of period	(75,862)		(75,862)
Accumulated other comprehensive (loss) income
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(76,803)	(91,530)	(78,960)	(93,194)
Gain (Loss) recognized in OCI, Net	(189)	58	950	810
Gain (Loss) reclassified from AOCI to income, Net	1,130	932	2,148	1,844
Total accumulated other comprehensive (loss) income, end of period	(75,862)	(90,540)	(75,862)	(90,540)
Changes in fair market value of hedges
Changes in AOCI, Gross
Gross, beginning of the period	1,332	1,308	289	116
Other Comprehensive Income (Loss), before Reclassifications, before Tax	240	(223)	1,397	819
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(154)	(15)	(268)	135
Gross, ending balance	1,418	1,070	1,418	1,070
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	(341)	(474)	(105)	(42)
Income tax (benefit), Gain (Loss) recognized in OCI	(54)	81	(315)	(297)
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	35	5	60	(49)
Income tax (benefit), ending of period	(360)	(388)	(360)	(388)
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	991	834	184	74
Gain (Loss) recognized in OCI, Net	186	(142)	1,082	522
Gain (Loss) reclassified from AOCI to income, Net	(119)	(10)	(208)	86
Total accumulated other comprehensive (loss) income, end of period	1,058	682	1,058	682
Changes in unrealized pension cost
Changes in AOCI, Gross
Gross, beginning of the period	(128,672)	(150,322)	(130,096)	(151,618)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	1,617	1,466	3,041	2,762
Gross, ending balance	(127,055)	(148,856)	(127,055)	(148,856)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	52,520	60,192	52,837	60,672
Income tax (benefit), Gain (Loss) recognized in OCI	0	0	0	0
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	(368)	(524)	(685)	(1,004)
Income tax (benefit), ending of period	52,152	59,668	52,152	59,668
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(76,152)	(90,130)	(77,259)	(90,946)
Gain (Loss) recognized in OCI, Net	0	0	0	0
Gain (Loss) reclassified from AOCI to income, Net	1,249	942	2,356	1,758
Total accumulated other comprehensive (loss) income, end of period	(74,903)	(89,188)	(74,903)	(89,188)
Cumulative translation adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(1,747)	(2,328)	(1,985)	(2,414)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(368)	196	(130)	282
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0	0
Gross, ending balance	(2,115)	(2,132)	(2,115)	(2,132)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	105	94	100	92
Income tax (benefit), Gain (Loss) recognized in OCI	(7)	4	(2)	6
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	0	0	0	0
Income tax (benefit), ending of period	98	98	98	98
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, beginning of period	(1,642)	(2,234)	(1,885)	(2,322)
Gain (Loss) recognized in OCI, Net	(375)	200	(132)	288
Gain (Loss) reclassified from AOCI to income, Net	0	0	0	0
Total accumulated other comprehensive (loss) income, end of period	$ (2,017)	$ (2,034)	$ (2,017)	$ (2,034)