Employee Benefit Plans Benefit Obligation And Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Change in Benefit Obligation:
Obligation at beginning of period	$ 696,796	$ 646,032
Service cost	11,776	10,994
Interest cost	24,420	25,633
Actuarial loss (gain)	(53,496)	41,719
Settlements	0	0
Benefits Paid	(29,870)	(27,582)
Benefit Obligation at End of Period	649,626	696,796	$ 646,032
Change in Fair Value of Plan Assets:
Employer contributions	10,600	10,000	9,800
Amounts Recognized in the Balance Sheet Consist of:
Noncurrent asset	2,672	2,535
Total Assets	2,672	2,535
Current liability	0	0
Noncurrent liability	(126,988)	(112,823)
Total Liabilities	(126,988)	(112,823)
Net amount recognized	(124,316)	(110,288)
Amounts recognized in AOCL consist of:
Prior service cost	0	0
Net actuarial gain	0	0
Total	(116,425)	(105,549)
Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	592,500	634,400
Accumulated benefit obligation	592,500	634,400
Fair value of plan assets	466,700	522,700
Pension Plan [Member] | Pension Costs [Member]
Amounts Recognized in Regulatory Assets Consist of:
Prior service (cost) credit	0	(4)
Net actuarial loss	(116,425)	(105,545)
Pension Plan [Member] | Changes Measurement [Member]
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	586,508	524,637
Return on plan assets	(40,528)	80,253
Employer contributions	9,200	9,200
Benefits Paid	(29,870)	(27,582)
Fair value of plan assets at end of period	525,310	586,508	524,637
Funded Status	(124,316)	(110,288)
Other Postretirement Benefits Plan [Member]
Change in Benefit Obligation:
Obligation at beginning of period	22,921	26,217
Service cost	398	456
Interest cost	578	715
Actuarial loss (gain)	(1,903)	(1,884)
Settlements	390	390
Benefits Paid	(1,773)	(2,973)
Benefit Obligation at End of Period	20,611	22,921	26,217
Amounts Recognized in the Balance Sheet Consist of:
Noncurrent asset	4,565	5,061
Total Assets	4,565	5,061
Current liability	(2,271)	(3,353)
Noncurrent liability	(4,235)	(4,249)
Total Liabilities	(6,506)	(7,602)
Net amount recognized	(1,941)	(2,541)
Amounts recognized in AOCL consist of:
Prior service cost	(548)	(698)
Net actuarial gain	1,260	(1,079)
Total	6,724	8,601
Other Postretirement Benefits Plan [Member] | Pension Costs [Member]
Amounts Recognized in Regulatory Assets Consist of:
Prior service (cost) credit	7,922	9,955
Net actuarial loss	(1,910)	(1,735)
Other Postretirement Benefits Plan [Member] | Changes Measurement [Member]
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	20,380	18,605
Return on plan assets	(866)	2,690
Employer contributions	929	2,058
Benefits Paid	(1,773)	(2,973)
Fair value of plan assets at end of period	18,670	20,380	$ 18,605
Funded Status	$ (1,941)	$ (2,541)