Pension and Other Postretirement Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets Aggregate Projected Benefit Obligation Qualified Plans	$ 451,200,000		$ 362,400,000
Defined Benefit Plan, Fair Value of Plan Assets	279,164,000		267,062,000
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss In Next Fiscal Year Regulatory	17,000,000
Defined Benefit Plan Amortization Of Net Gains Losses Regulatory	16,600,000
Defined Benefit Plan Amortization Of Net Prior Service Cost Credit Regulatory	400,000
Multiemployer Plan, Period Contributions	400,000		500,000		400,000
Multiemployer Plan, Percentage of Contributions	4% to 5%
Multiemployer Plan, Withdrawal Liability Cost			8,300,000
Multiemployer Plans, Withdrawal Obligation	8,100,000
Multiemployer Plans, Withdrawal Payment Per Year For Next 20 Years	600,000
Defined Contribution Plan, Cost Recognized	3,400,000		2,200,000		2,200,000
Defined Benefit Obligations Non Qualified Supplemental	36,100,000		28,700,000
Qualified Defined Benefit Plans Benefit Obligation Underfunded	172,000,000
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	(7,000)		(7,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, beore Tax	1,091,000		1,550,000
Accumulated other comprehensive loss	(10,076,000)		(6,358,000)		(9,291,000)
Total Amounts Reclassified Into Accumulated Other Comprehensive Income	(7,221,000)		3,302,000
Other Comprehensive Income (Loss), Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service (Cost) Credit, Tax	2,419,000		(1,912,000)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(3,718,000)		2,933,000
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Amortization of Net Gains (Losses)	(2,200,000)
Pension and Other Postretirement Benefit Contributions [Abstract]
Qualified Defined Benefit Pension Plan Contributions	10,500,000
Payroll Overhead Charge to Construction Work Orders	25% to 35%
Defined Benefit Plan, Health Care Cost Trend Rate For Pre-65 Population Assumed for Next Fiscal Year	8.00%
Defined Benefit Plan, Health Care Cost Trend Rate For Post-65 Population Assumed for Next Fiscal Year	11.75%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	2022
Other Comprehensive Income Total Reclassifications Before Tax	(6,137,000)		4,845,000
Qualified Contributions Expected During Next Fiscal Year	15,000,000
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	62,000
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	(55,000)
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	1,260,000
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	(965,000)
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Asset Receivable Or Payable Accrued Interest And Dividend Income	510,000		468,000
Plan Asset Receivable Or Payable Due From Broker Securities Sold	1,694,000		1,154,000
Total Pension Plan Asset Receivables	2,204,000		1,622,000
Plan Asset Receivable Or Payable Due From Broker Securities Purchased	179,000		1,178,000
Defined Benefit Plan, Fair Value of Plan Assets	279,164,000		267,062,000
Plan Asset Target Allocation [Abstract]
US Large Cap Equity Pension Plan Asset Target Allocation	18.00%
US Small Mid Cap Equity Pension Plan Asset Target Allocation	10.00%
Non US Equity Pension Plan Asset Target Allocation	18.00%
Emerging Markets Equity Pension Plan Asset Target Allocation	5.00%
Long Government Credit Pension Plan Asset Target Allocation	20.00%
High Yield Pension Plan Asset Target Allocation	5.00%
Emerging Market Debt Pension Plan Asset Target Allocation	5.00%
Real Estate Funds Pension Plan Asset Target Allocation	7.00%
Absolute Return Strategy Pension Plan Asset Target Allocation	12.00%
Defined Benefit Plan Fair Value Of Plan Assets By Measurement Table [Abstract]
US Large Cap Equity Pension Assets	39,527,000		39,203,000
US Small Mid Cap Equity Pension Assets	27,257,000		30,520,000
Non US Equity Pension Assets	33,590,000		33,984,000
Emerging Markets Equity Pension Assets	7,145,000		7,405,000
Fixed Income Pension Assets	598,000		367,000
Long Government Credit Pension Assets	80,819,000		65,915,000
High Yield Bonds Pension Assets	13,087,000		12,890,000
Emerging Market Debt Pension Assets	9,133,000		9,987,000
Real Estate Funds Pension Assets	18,890,000		16,559,000
Absolute Return Strategy Pension Assets	37,065,000		35,339,000
Real Return Strategy Pension Assets	8,308,000		13,031,000
Cash And Cash Equivalents Pension Assets	1,720,000		1,418,000
Total Pension Asset Investments Net Of Receivables And Payables	277,139,000		266,618,000
Pension Plans, Defined Benefit [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	279,164,000		267,062,000		249,603,000
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	487,278,000		391,089,000		435,889,000
Defined Benefit Plan, Service Cost	7,213,000		8,698,000		8,047,000
Defined Benefit Plan, Interest Cost	18,198,000		16,400,000		17,295,000
Defined Benefit Plan, Actuarial Gain (Loss)	90,710,000		(51,043,000)
Defined Benefit Plan, Benefits Paid	19,932,000		18,855,000		18,195,000
Defined Benefit Plan, Actual Return on Plan Assets	19,957,000		22,872,000
Defined Benefit Plan, Contributions by Employer	12,077,000		13,442,000
Defined Benefit Plan, Funded Status of Plan	(208,114,000)		(124,027,000)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	7,213,000		8,698,000		8,047,000
Defined Benefit Plan, Interest Cost	18,198,000		16,400,000		17,295,000
Defined Benefit Plan, Expected Return on Plan Assets	(19,496,000)		(18,721,000)		(19,082,000)
Defined Benefit Plan Amortization Of Transition Obligations	0		0		0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	223,000		223,000		195,000
Defined Benefit Plan, Amortization of Net Gains (Losses)	10,914,000		18,294,000		15,631,000
Defined Benefit Plan Net Periodic Benefit Cost	17,052,000		24,894,000		22,086,000
Defined Benefit Plan Amount Allocated To Construction	(4,625,000)		(6,712,000)		(5,820,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	(4,578,000)	[1]	(9,115,000)	[1]	(7,876,000)	[1]
Defined Benefit Plan Net Amount Charged To Expense	7,849,000		9,067,000		8,390,000
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.71%		3.84%		4.51%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.50%		7.50%		8.00%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.85%		4.73%		3.85%
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Low Range	3.25%		3.25%		3.25%
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation High Range	5.00%		5.00%		5.00%
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Low Range	3.25%		3.25%		3.25%
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation High Range	5.00%		5.00%		5.00%
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Expected Long Term Return On Assets	7.50%		7.50%		7.50%
Pension and Other Postretirement Benefit Contributions [Abstract]
Qualified Defined Benefit Pension Plan Contributions	12,077,000		13,907,000
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	16,567,000
Defined Benefit Plan, Benefits Paid	19,932,000		18,855,000		18,195,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	20,315,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	20,993,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	21,784,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	22,799,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	24,162,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	137,839,000
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	279,164,000		267,062,000		249,603,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0		0
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	32,072,000		28,754,000		33,119,000
Defined Benefit Plan, Service Cost	483,000		656,000		592,000
Defined Benefit Plan, Interest Cost	1,252,000		1,157,000		1,267,000
Defined Benefit Plan, Actuarial Gain (Loss)	3,454,000		(4,283,000)
Defined Benefit Plan, Benefits Paid	1,871,000		1,895,000		1,971,000
Defined Benefit Plan, Actual Return on Plan Assets	0		0
Defined Benefit Plan, Contributions by Employer	1,871,000		1,895,000
Defined Benefit Plan, Funded Status of Plan	(32,072,000)		(28,754,000)
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	3,454,000		(4,283,000)		3,182,000
Regulatory Amortization Of Defined Benefit Plan Net Transition Asset Obligation Recognized In Net Periodic Benefit Cost Before Tax	0		0		(411,000)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	(197,000)		(197,000)		(197,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, beore Tax	(221,000)		(733,000)		(435,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	3,036,000		(5,213,000)		2,139,000
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost	483,000		656,000		592,000
Defined Benefit Plan, Interest Cost	1,252,000		1,157,000		1,267,000
Defined Benefit Plan, Expected Return on Plan Assets	0		0		0
Defined Benefit Plan Amortization Of Transition Obligations	0		0		411,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	197,000		197,000		197,000
Defined Benefit Plan, Amortization of Net Gains (Losses)	221,000		734,000		435,000
Defined Benefit Plan Net Periodic Benefit Cost	2,153,000		2,744,000		2,902,000
Defined Benefit Plan Amount Allocated To Construction	(702,000)		(856,000)		(882,000)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	0	[1]	0	[1]	0	[1]
Defined Benefit Plan Net Amount Charged To Expense	1,451,000		1,888,000		2,020,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	488,000		685,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	7,898,000		4,665,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	8,386,000		5,350,000
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.45%		3.56%		4.33%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.74%		4.45%		3.56%
Pension and Other Postretirement Benefit Contributions [Abstract]
Qualified Defined Benefit Pension Plan Contributions	1,871,000				1,895,000
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	1,848,000
Defined Benefit Plan, Benefits Paid	1,871,000		1,895,000		1,971,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	1,848,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	1,918,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	1,955,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	2,007,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	2,075,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	10,412,000
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	0		0		0
Qualified Pension Plans, Defined Benefit [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	279,200,000		267,100,000
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	83,027,000		(51,892,000)		26,504,000
Regulatory Amortization Of Defined Benefit Plan Net Transition Asset Obligation Recognized In Net Periodic Benefit Cost Before Tax	0		0		0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	(230,000)		(230,000)		(230,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, beore Tax	(9,823,000)		(16,744,000)		(14,482,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	72,974,000		(68,866,000)		11,792,000
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	637,000		867,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	192,846,000		119,638,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	193,483,000		120,505,000
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	279,200,000		267,100,000
Non-Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	7,221,000		(3,302,000)		3,511,000
Regulatory Amortization Of Defined Benefit Plan Net Transition Asset Obligation Recognized In Net Periodic Benefit Cost Before Tax	0		0		0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax	7,000		7,000		35,000
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, beore Tax	(1,091,000)		(1,550,000)		(1,150,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	6,137,000		(4,845,000)		2,396,000
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	2,000		(5,000)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	16,604,000		10,475,000
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	16,606,000		10,470,000
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Fair Value Of Plan Assets By Measurement Table [Abstract]
US Large Cap Equity Pension Assets	39,405,000		39,124,000
US Small Mid Cap Equity Pension Assets	27,172,000		30,465,000
Non US Equity Pension Assets	16,369,000		16,782,000
Emerging Markets Equity Pension Assets	0		7,405,000
Fixed Income Pension Assets	0		0
Long Government Credit Pension Assets	40,584,000		33,152,000
High Yield Bonds Pension Assets	0		0
Emerging Market Debt Pension Assets	9,133,000		9,987,000
Real Estate Funds Pension Assets	18,890,000		16,559,000
Absolute Return Strategy Pension Assets	0		0
Real Return Strategy Pension Assets	8,308,000		13,031,000
Cash And Cash Equivalents Pension Assets	0		0
Total Pension Asset Investments Net Of Receivables And Payables	159,861,000		166,505,000
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Fair Value Of Plan Assets By Measurement Table [Abstract]
US Large Cap Equity Pension Assets	122,000		79,000
US Small Mid Cap Equity Pension Assets	85,000		55,000
Non US Equity Pension Assets	17,221,000		17,202,000
Emerging Markets Equity Pension Assets	7,145,000		0
Fixed Income Pension Assets	598,000		367,000
Long Government Credit Pension Assets	40,235,000		32,763,000
High Yield Bonds Pension Assets	13,087,000		12,890,000
Emerging Market Debt Pension Assets	0		0
Real Estate Funds Pension Assets	0		0
Absolute Return Strategy Pension Assets	37,065,000		35,339,000
Real Return Strategy Pension Assets	0		0
Cash And Cash Equivalents Pension Assets	1,720,000		1,418,000
Total Pension Asset Investments Net Of Receivables And Payables	117,278,000		100,113,000
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Fair Value Of Plan Assets By Measurement Table [Abstract]
US Large Cap Equity Pension Assets	0		0
US Small Mid Cap Equity Pension Assets	0		0
Non US Equity Pension Assets	0		0
Emerging Markets Equity Pension Assets	0		0
Fixed Income Pension Assets	0		0
Long Government Credit Pension Assets	0		0
High Yield Bonds Pension Assets	0		0
Emerging Market Debt Pension Assets	0		0
Real Estate Funds Pension Assets	0		0
Absolute Return Strategy Pension Assets	0		0
Real Return Strategy Pension Assets	0		0
Cash And Cash Equivalents Pension Assets	0		0
Total Pension Asset Investments Net Of Receivables And Payables	$ 0		$ 0

[1] The deferral of certain pension expenses above or below the amount set in rates was approved by the OPUC, with recovery of these deferred amounts through the implementation of a balancing account, which includes the expectation of lower net periodic benefit costs in future years. Deferred pension expense balances include accrued interest at the utility’s authorized rate of return, with the equity portion of the interest being deferred until amounts are collected in rates. See Note 2.