Components of Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ (1,304,953)	$ (1,226,831)
Effect of pension settlement		(31,811)
Balance at end of period	(1,526,133)	(1,304,953)
Pension Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	79,025	117,028
Net (gain) loss arising during the period	(19,147)	5,306
Effect of pension settlement		(31,811)
Amounts reclassified from AOCL to earnings	(10,299)	(11,498)
Balance at end of period	49,579	79,025
Other Postretirement Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	14,783	10,331
Net (gain) loss arising during the period	(12,378)	4,747
Amounts reclassified from AOCL to earnings	(615)	(295)
Balance at end of period	1,790	14,783
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	27,181	20,000
Net (gain) loss arising during the period	(26,206)	14,632
Amounts reclassified from AOCL to earnings	(9,106)	(7,451)
Balance at end of period	(8,131)	27,181
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	120,989	147,359
Balance at end of period	$ 43,238	$ 120,989