Retirement Benefits Change in Net Benefit Obligation (Details) - Parent Company [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period			$ 774,305	$ 677,643	$ 677,643
Service cost	$ 6,172	$ 5,287	12,169	10,574	22,656
Interest cost	6,292	7,216	12,590	14,433	28,913
Actuarial loss (gain)			1,134		84,272
Benefits paid			(23,990)		(36,740)
Medicare part D subsidy received			0		0
Administrative Expense			0		(2,439)
Benefit obligation at end of period	776,208		776,208		774,305
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period			63,000	55,708	55,708
Service cost	176	256	404	512	1,023
Interest cost	362	578	740	1,157	2,314
Actuarial loss (gain)			(478)		6,756
Benefits paid			(17,643)		(2,801)
Medicare part D subsidy received			0		0
Administrative Expense			0		0
Benefit obligation at end of period	46,023		46,023		63,000
Other Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period			11,627	10,636	10,636
Amendments			0		(9,049)
Service cost	46	16	95	33	61
Interest cost	93	$ 112	184	$ 224	410
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment			0		(7,486)
Actuarial loss (gain)			34		(287)
Benefits paid			(494)		(982)
Medicare part D subsidy received			187		226
Administrative Expense			0		0
Benefit obligation at end of period	$ 11,633		11,633		11,627
Qualified Plan [Member] | Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Amendments			0		0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment			0		0
Nonqualified Plan [Member] | Qualified Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment			0		0
Nonqualified Plan [Member] | Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Amendments			$ 0		$ 0