Accumulated Other Comprehensive (Loss) Income - Summary of Components of Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Foreign currency transaction loss
Foreign currency transaction gain (loss)	$ 892	$ 829	$ (379)	$ 355
AOCI Attributable to Parent, Net of Tax
Total accumulated other comprehensive (loss) income, end of period	(93,155)		(93,155)			$ (91,726)
Accumulated Other Comprehensive Earnings/(Loss)
AOCI Attributable to Parent, Net of Tax
Gain (Loss) recognized in OCI, Net	192	(62)	(4,144)	274
Gain (Loss) reclassified from AOCI to income, Net	1,647	707	2,715	1,562
Total accumulated other comprehensive (loss) income, end of period	(93,155)	(95,903)	(93,155)	(95,903)	$ (94,994)	(91,726)	$ (96,548)	$ (97,739)
Changes in fair market value of hedges
Changes in AOCI, Gross
Gross, beginning of the period	(5,044)	1,416	659	1,316
Other Comprehensive Income (Loss), before Reclassifications, before Tax	250	32	(5,172)	348
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	555	(412)	274	(628)
Gross, ending balance	(4,239)	1,036	(4,239)	1,036
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	1,139	(320)	(150)	(298)
Income tax (benefit), Gain (Loss) recognized in OCI	(44)	(7)	1,181	(78)
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	(117)	93	(53)	142
Income tax (benefit), ending of period	978	(234)	978	(234)
AOCI Attributable to Parent, Net of Tax
Gain (Loss) recognized in OCI, Net	206	25	(3,991)	270
Gain (Loss) reclassified from AOCI to income, Net	438	(319)	221	486
Total accumulated other comprehensive (loss) income, end of period	(3,261)	802	(3,261)	802	(3,905)	509	1,096	1,018
Changes in unrealized pension cost
Changes in AOCI, Gross
Gross, beginning of the period	(122,480)	(131,135)	(124,140)	(132,454)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	1,574	1,325	3,234	2,644
Gross, ending balance	(120,906)	(129,810)	(120,906)	(129,810)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	33,643	35,596	34,018	35,893
Income tax (benefit), Gain (Loss) recognized in OCI	0	0	0	0
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	(365)	(299)	(740)	(596)
Income tax (benefit), ending of period	33,278	35,297	33,278	35,297
AOCI Attributable to Parent, Net of Tax
Gain (Loss) recognized in OCI, Net	0	0	0	0
Gain (Loss) reclassified from AOCI to income, Net	1,209	1,026	2,494	2,048
Total accumulated other comprehensive (loss) income, end of period	(87,628)	(94,513)	(87,628)	(94,513)	(88,837)	(90,122)	(95,539)	(96,561)
Cumulative translation adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,252)	(2,203)	(2,211)	(2,291)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(14)	(84)	(55)	4
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0	0	0
Gross, ending balance	(2,266)	(2,287)	(2,266)	(2,287)
Changes in AOCI, Income tax (benefit)
Income tax (benefit), beginning of period	0	98	98	95
Income tax (benefit), Gain (Loss) recognized in OCI	0	(3)	(98)	0
Income tax (benefit), Gain (Loss) reclassified from AOCI to income	0	0	0	0
Income tax (benefit), ending of period	0	95	0	95
AOCI Attributable to Parent, Net of Tax
Gain (Loss) recognized in OCI, Net	(14)	(87)	(153)	4
Gain (Loss) reclassified from AOCI to income, Net	0	0	0	0
Total accumulated other comprehensive (loss) income, end of period	$ (2,266)	$ (2,192)	$ (2,266)	$ (2,192)	$ (2,252)	$ (2,113)	$ (2,105)	$ (2,196)