Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (134,898)
Other comprehensive income (loss)		7,099	$ (19,084)	$ 40,579
Ending balance		(150,893)	(134,898)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(14,579)	(7,054)
Other comprehensive income (loss), before reclassifications		(1,772)	(7,525)
Reclassification to net income		1,772	9,255
Ending balance		(16,351)	(14,579)	(7,054)
Pension and other post-retirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(120,319)	(108,760)
Other comprehensive income (loss)	[1]	8,871	(11,559)
Ending balance	[1]	(134,542)	(120,319)	$ (108,760)
Accumulated Defined Benefit Plan & SERP, Stranded Tax Effects [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	(23,094)	0
Amortization of net loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	11,971	8,800
Reclassification from AOCI, tax		(3,534)	(2,818)
Change in net gain
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification to net income	[1]	(3,100)	(20,359)
Reclassification from AOCI, tax		915	6,519
U.K. Composites [Member] | Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax		$ 0	$ 1,730

[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)