Employee Benefit Plans (Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Changes in AOCL [Roll Forward]
Beginning balance	$ 1,899,800	$ 2,303,800	$ 2,715,000
Net actuarial gain (loss)	43,700	16,300	(23,500)
Recognition of prior service credit amortization in income	(200)	(200)	(200)
Recognition of actuarial loss amortization in income	4,600	6,000	5,900
Curtailment gain	0	0	1,700
Settlement cost	9,500	2,600	1,000
Total other comprehensive income (loss)	61,100	28,200	(21,100)
Ending balance	1,684,900	1,899,800	2,303,800
Pension Benefits
Changes in AOCL [Roll Forward]
Beginning balance	(92,800)	(117,800)	(104,700)
Net actuarial gain (loss)	37,100	17,200	(21,000)
Recognition of prior service credit amortization in income	(200)	(200)	(200)
Recognition of actuarial loss amortization in income	4,200	5,400	5,400
Curtailment gain	0	0	1,700
Settlement cost	9,500	2,600	1,000
Total other comprehensive income (loss)	50,600	25,000	(13,100)
Ending balance	(42,200)	(92,800)	(117,800)
Other Postretirement Benefits
Changes in AOCL [Roll Forward]
Beginning balance	(10,700)	(10,400)	(8,400)
Net actuarial gain (loss)	6,600	(900)	(2,500)
Recognition of prior service credit amortization in income	0	0	0
Recognition of actuarial loss amortization in income	400	600	500
Curtailment gain	0	0	0
Settlement cost	0	0	0
Total other comprehensive income (loss)	7,000	(300)	(2,000)
Ending balance	$ (3,700)	$ (10,700)	$ (10,400)