Pension Plans And Other Postretirement Benefit Plans (Change in Benefit Obligation and Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Plan, Current	$ (8,826)	$ (9,151)
Liability, Defined Benefit Plan, Noncurrent	(212,006)	(222,537)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax	(10,259)	(7,866)
Pension Plan And SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year	671,629	716,561
Service cost	19,755	21,614	$ 20,406
Interest cost	28,417	26,096	27,898
Actuarial (gain)/loss	57,829	(48,641)
Benefits paid	(35,248)	(44,001)
Benefit obligation as of end of year	742,382	671,629	716,561
Fair value of plan assets as of beginning of year	544,051	605,652
Actual return on plan assets	109,942	(40,954)
Employer contributions	22,000	22,000
Benefits Paid	(33,930)	(42,647)
Fair value of plan assets as of end of year	642,063	544,051	605,652
Funded status	(100,319)	(127,578)
Liability, Defined Benefit Plan, Current	(1,602)	(1,477)
Liability, Defined Benefit Plan, Noncurrent	(98,717)	(126,101)
Liability, Defined Benefit Plan	(100,319)	(127,578)
Accumulated pension benefit obligation	644,004	586,398
Unrecognized prior service cost	2,105	2,308
Unrecognized net actuarial loss	114,368	138,516
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Before Regulatory Asset, Net of Tax	116,473	140,824
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax	9,078	7,587
Less regulatory asset	$ (107,395)	$ (133,237)
Discount rate for benefit obligation	3.85%	4.31%
Discount rate for annual expense	4.31%	3.71%
Expected long-term return on plan assets	5.90%	5.50%
Rate of compensation increase	4.66%	4.67%
Expected return on plan assets	$ (31,763)	$ (33,018)	(31,626)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year	134,053	132,947
Service cost	3,006	3,188	3,220
Interest cost	5,598	4,831	5,490
Actuarial (gain)/loss	23,344	(610)
Benefits paid	(6,705)	(6,303)
Benefit obligation as of end of year	159,296	134,053	132,947
Fair value of plan assets as of beginning of year	36,852	37,953
Actual return on plan assets	8,001	(1,101)
Employer contributions	0	0
Benefits Paid	0	0
Fair value of plan assets as of end of year	44,853	36,852	37,953
Funded status	(114,443)	(97,201)
Liability, Defined Benefit Plan, Current	(640)	(580)
Liability, Defined Benefit Plan, Noncurrent	(113,803)	(96,621)
Liability, Defined Benefit Plan	(114,443)	(97,201)
Accumulated pension benefit obligation	0	0
Unrecognized prior service cost	(4,400)	(5,230)
Unrecognized net actuarial loss	63,101	52,441
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Before Regulatory Asset, Net of Tax	58,701	47,211
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax	1,181	279
Less regulatory asset	$ (57,520)	$ (46,932)
Discount rate for benefit obligation	3.89%	4.32%
Discount rate for annual expense	4.32%	3.72%
Expected long-term return on plan assets	5.70%	5.20%
Expected return on plan assets	$ (2,101)	$ (1,973)	$ (1,899)
Other Postretirement Benefits [Member] | Pre-Age 65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend - initial	5.75%	6.00%
Medical cost trend - ultimate	5.00%	5.00%
Ultimate medical cost trend year	2023	2023
Other Postretirement Benefits [Member] | Post-Age 65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend - initial	6.50%	6.25%
Medical cost trend - ultimate	5.00%	5.00%
Ultimate medical cost trend year	2026	2024
Retirees [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year	$ 63,796
Benefit obligation as of end of year	72,816	$ 63,796
Fully eligible employees [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year	29,902
Benefit obligation as of end of year	34,545	29,902
Other participants [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year	40,355
Benefit obligation as of end of year	$ 51,935	$ 40,355