Employee Benefit Plans Benefit Obligation And Funded Status (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plan [Member]
Change in Benefit Obligation:
Obligation beginning of period	$ 567,866,000	$ 609,643,000
Service cost	10,830,000	13,465,000
Interest cost	26,147,000	22,719,000
Actuarial (gain) loss	107,023,000	(54,671,000)
Settlements	0	0
Benefits paid	(23,422,000)	(23,290,000)
Benefit obligation end of period	688,444,000	567,866,000	609,643,000
Change in Fair Value of Plan Assets:
Employer contributions	8,700,000	7,800,000	7,200,000
Benefits paid	(23,422,000)	(23,290,000)
Amounts recognized in balance sheet consist of:
Current liability	0	0
Noncurrent liability	(132,393,000)	(51,514,000)
Net amount recognized	(132,393,000)	(51,514,000)
Amounts recognized in AOCI consist of:
Prior service cost	0	0
Net actuarial gain	0	0
Total	(153,770,000)	(72,525,000)
Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	688,400,000	567,900,000
Accumulated benefit obligation	685,000,000	565,000,000
Fair value of plan assets	556,100,000	516,400,000
Pension Plan [Member] | Pension Costs [Member]
Amounts recognized in regulatory assets consist of:
Prior service (cost) credit	(502,000)	(748,000)
Net actuarial loss	(153,268,000)	(71,777,000)
Pension Plan [Member] | Changes Measurement [Member]
Change in Benefit Obligation:
Benefits paid	(23,422,000)	(23,290,000)
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	516,352,000	472,936,000
Return on plan assets	52,921,000	55,006,000
Employer contributions	10,200,000	11,700,000
Benefits paid	(23,422,000)	(23,290,000)
Fair value of plan assets at end of period	556,051,000	516,352,000
Funded Status	(132,393,000)	(51,514,000)
Other Postretirement Benefit Plan [Member]
Change in Benefit Obligation:
Obligation beginning of period	30,084,000	34,040,000
Service cost	465,000	541,000
Interest cost	859,000	877,000
Actuarial (gain) loss	958,000	(3,156,000)
Settlements	690,000	0
Benefits paid	(3,052,000)	(2,218,000)
Benefit obligation end of period	30,004,000	30,084,000
Change in Fair Value of Plan Assets:
Benefits paid	(3,052,000)	(2,218,000)
Amounts recognized in balance sheet consist of:
Current liability	(1,169,000)	(1,178,000)
Noncurrent liability	(10,795,000)	(10,723,000)
Net amount recognized	(11,964,000)	(11,901,000)
Amounts recognized in AOCI consist of:
Prior service cost	(1,151,000)	(1,302,000)
Net actuarial gain	(409,000)	(971,000)
Total	10,593,000	12,167,000
Other Postretirement Benefit Plan [Member] | Pension Costs [Member]
Amounts recognized in regulatory assets consist of:
Prior service (cost) credit	17,098,000	19,247,000
Net actuarial loss	(4,945,000)	(4,807,000)
Other Postretirement Benefit Plan [Member] | Changes Measurement [Member]
Change in Benefit Obligation:
Benefits paid	(3,052,000)	(2,218,000)
Change in Fair Value of Plan Assets:
Fair value of plan assets at beginning of period	18,183,000	15,893,000
Return on plan assets	1,391,000	2,662,000
Employer contributions	1,518,000	1,846,000
Benefits paid	(3,052,000)	(2,218,000)
Fair value of plan assets at end of period	18,040,000	18,183,000
Funded Status	$ (11,964,000)	$ (11,901,000)