Employee Benefit Plans Schedule of Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in AOCL [Roll Forward]
Beginning balance	$ 2,454,738	$ 2,637,779	$ 2,715,028	$ 2,643,434
Net actuarial loss	0	0	(333)	(10,913)
Curtailment gain	0	0	1,703	0
Recognition of prior service credit amortization in income	(46)	(46)	(136)	(136)
Recognition of actuarial loss amortization in income	1,473	1,412	4,462	4,385
Recognition of settlement cost in income	0	439	969	2,499
Ending balance	2,388,444	2,674,456	2,388,444	2,674,456
Pension Plan [Member]
Changes in AOCL [Roll Forward]
Net actuarial loss			813	(10,029)
Curtailment gain			1,703	0
Recognition of prior service credit amortization in income	(46)	(46)	(136)	(136)
Recognition of actuarial loss amortization in income	1,346	1,352	4,080	4,137
Recognition of settlement cost in income	0	439	969	2,499
Other Postretirement Benefits Plan [Member]
Changes in AOCL [Roll Forward]
Net actuarial loss			(1,146)	(884)
Curtailment gain			0	0
Recognition of prior service credit amortization in income	0	0	0	0
Recognition of actuarial loss amortization in income	127	60	382	248
Recognition of settlement cost in income	0	0	0	0
Accumulated Other Comprehensive Loss | Pension Plan [Member]
Changes in AOCL [Roll Forward]
Beginning balance	(98,610)	(93,876)	(104,739)	(88,602)
Ending balance	(97,310)	(92,131)	(97,310)	(92,131)
Accumulated Other Comprehensive Loss | Other Postretirement Benefits Plan [Member]
Changes in AOCL [Roll Forward]
Beginning balance	(9,269)	(6,105)	(8,378)	(5,409)
Ending balance	$ (9,142)	$ (6,045)	$ (9,142)	$ (6,045)