Employee Benefit Plans Benefit Obligation And Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Change in Benefit Obligation:
Obligation at beginning of period	$ 628,883	$ 688,444
Service cost	11,759	12,362
Interest cost	26,210	26,174
Plan amendments	0	0
Actuarial loss (gain)	7,006	(47,351)
Settlements	0	0
Benefits paid	(27,826)	(50,746)
Benefit Obligation at End of Period	646,032	628,883	$ 688,444
Change in Fair Value of Plan Assets:
Employer contributions	9,800	9,500	8,700
Benefits paid	(27,826)	(50,746)
Amounts Recognized in the Balance Sheet Consist of:
Current liability	0	0
Noncurrent liability	(121,395)	(128,839)
Net amount recognized	(121,395)	(128,839)
Amounts recognized in AOCL consist of:
Prior service cost	0	0
Net actuarial gain	0	0
Total	(127,962)	(142,560)
Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	646,000	628,900
Accumulated benefit obligation	643,600	626,000
Fair value of plan assets	524,600	500,000
Pension Plan [Member] | Pension Costs [Member]
Amounts Recognized in Regulatory Assets Consist of:
Prior service (cost) credit	(9)	(255)
Net actuarial loss	(127,953)	(142,305)
Pension Plan [Member] | Changes Measurement [Member]
Change in Benefit Obligation:
Benefits paid	(27,826)	(50,746)
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	500,044	556,051
Return on plan assets	39,719	(15,461)
Employer contributions	12,700	10,200
Benefits paid	(27,826)	(50,746)
Fair value of plan assets at end of period	524,637	500,044	556,051
Funded Status	(121,395)	(128,839)
Other Postretirement Benefit Plan [Member]
Change in Benefit Obligation:
Obligation at beginning of period	28,652	30,004
Service cost	492	526
Interest cost	795	786
Plan amendments	0	1,045
Actuarial loss (gain)	(71)	(616)
Settlements	390	390
Benefits paid	(4,041)	(3,483)
Benefit Obligation at End of Period	26,217	28,652	30,004
Change in Fair Value of Plan Assets:
Benefits paid	(4,041)	(3,483)
Amounts Recognized in the Balance Sheet Consist of:
Current liability	(1,789)	(2,584)
Noncurrent liability	(5,823)	(8,096)
Net amount recognized	(7,612)	(10,680)
Amounts recognized in AOCL consist of:
Prior service cost	(849)	(1,000)
Net actuarial gain	38	(102)
Total	6,438	7,700
Other Postretirement Benefit Plan [Member] | Pension Costs [Member]
Amounts Recognized in Regulatory Assets Consist of:
Prior service (cost) credit	11,988	14,021
Net actuarial loss	(4,739)	(5,219)
Other Postretirement Benefit Plan [Member] | Changes Measurement [Member]
Change in Benefit Obligation:
Benefits paid	(4,041)	(3,483)
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	17,972	18,040
Return on plan assets	1,277	0
Employer contributions	3,397	3,415
Benefits paid	(4,041)	(3,483)
Fair value of plan assets at end of period	18,605	17,972	$ 18,040
Funded Status	$ (7,612)	$ (10,680)