Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (150,893)
Other comprehensive income (loss)		20,072	$ 7,099	$ (19,084)
Ending balance		(130,821)	(150,893)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(16,351)	(14,579)
Other comprehensive income (loss), before reclassifications		15,634	(1,772)
Reclassification to net income		(15,634)	1,772
Ending balance		(717)	(16,351)	(14,579)
Pension and other post-retirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(134,542)	(120,319)
Other comprehensive income (loss)	[1]	4,438	8,871
Ending balance	[1]	(130,104)	(134,542)	$ (120,319)
Accumulated Defined Benefit Plan & SERP, Stranded Tax Effects [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	0	(23,094)
Amortization of net loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	4,434	11,971
Reclassification from AOCI, tax		1,314	3,534
Change in net gain
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	4	(3,100)
Reclassification from AOCI, tax		$ 1	$ (915)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 17, Pension Plans for additional information)