Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Income or Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 933,900	$ 848,324
Other comprehensive income (loss) before reclassifications	24,658	(12,240)
Amounts reclassified to earnings	2,672	44,169
Net other comprehensive income (loss) for period	27,330	31,929
Ending Balance	1,020,755	933,900
AOCI, Pension and other postretirement benefit plans, tax	1,951	2,368	$ 9,984
AOCI, cumulative changes in net gain (loss) from cash flow hedges, tax	0	282	$ (106)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(46,905)	(78,834)
Ending Balance	(19,575)	(46,905)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(35,478)	(30,488)
Other comprehensive income (loss) before reclassifications	24,907	(4,990)
Amounts reclassified to earnings	0	0
Net other comprehensive income (loss) for period	24,907	(4,990)
Ending Balance	(10,571)	(35,478)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(10,455)	(48,700)
Other comprehensive income (loss) before reclassifications	1,255	(6,079)
Amounts reclassified to earnings	196	44,324
Net other comprehensive income (loss) for period	1,451	38,245
Ending Balance	(9,004)	(10,455)
Derivative Instrument Designated as Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(972)	354
Other comprehensive income (loss) before reclassifications	(1,504)	(1,171)
Amounts reclassified to earnings	2,476	(155)
Net other comprehensive income (loss) for period	972	(1,326)
Ending Balance	$ 0	$ (972)