Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 22, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss In Next Fiscal Year Regulatory		$ 13,300
Defined Benefit Plan Amortization Of Net Gains Losses Regulatory		13,500
Defined Benefit Plan Amortization Of Net Prior Service Cost Credit Regulatory		$ 200
Defined Benefit Plan, Health Care Cost Trend Rate For Pre-65 Population Assumed for Next Fiscal Year		7.50%
Defined Benefit Plan, Health Care Cost Trend Rate For Post-65 Population Assumed for Next Fiscal Year		7.50%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate, Decrease		4.75%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate					2024
Defined Contribution Plan, Cost Recognized		$ 3,700	$ 3,400	$ 2,200
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Accumulated Other Comprehensive loss, beginning of period		(10,076)
Accumulated Other Comprehensive loss, end of period		(7,162)	(10,076)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Amortization of loss		1,300
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		100
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components		(74)
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation		742
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation		(665)
Pension and Other Postretirement Benefit Contributions [Abstract]
Qualified Defined Benefit Pension Plan Contributions		$ 14,100
Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Net Periodic Benefit Costs Overhead Charge Percentage		25.00%
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Net Periodic Benefit Costs Overhead Charge Percentage		35.00%
Domestic Large Cap Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		18.00%
Domestic Small/Mid Cap Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		10.00%
Foreign Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		18.00%
Emerging Market Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		5.00%
Government Or Credit Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		20.00%
High Yield Bond Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		5.00%
Emerging Market Debt [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		5.00%
Real Estate Funds [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		7.00%
Absolute Return Strategy Investment Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Target Plan Asset Allocations		12.00%
Pension Costs [Member]
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Regulatory Assets Prior Service Cost					$ 406	$ 637
Regulatory Assets Actuarial Loss					176,894	192,846
Regulatory Assets					177,300	193,483
Postretirement Benefit Costs [Member]
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Regulatory Assets Prior Service Cost					(3,143)	488
Regulatory Assets Actuarial Loss					10,067	7,898
Regulatory Assets					6,924	8,386
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		$ 487,278	391,089	391,089	445,628	487,278	$ 391,089
Defined Benefit Plan, Fair Value of Plan Assets		279,164	267,062	267,062	249,338	279,164	$ 267,062
Defined Benefit Plan, Funded Status of Plan					$ (196,290)	$ (208,114)
Reconciliation of change in benefit obligation
Obligation at beginning of period		487,278	391,089
Defined Benefit Plan, Service Cost		8,267	7,213	8,698
Defined Benefit Plan, Interest Cost		18,360	18,198	16,400
Defined Benefit Plan, Plan Amendments	[1]	0	0
Defined Benefit Plan, Actuarial Loss		(32,354)	90,710
Defined Benefit Plan, Benefits Paid		35,923	19,932	18,855
Obligation and end of period		445,628	487,278	391,089
Reconciliation of change in plan assets
Fair value of plan assets, beginning of period		279,164	267,062
Defined Benefit Plan, Actual Return on Plan Assets		(9,599)	19,957
Defined Benefit Plan, Contributions by Employer		15,696	12,077
Defined Benefit Plan, Benefits Paid		35,923	19,932	18,855
Fair value of plan assets, end of period		249,338	279,164	267,062
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Regulatory assets defined benefit pension actuarial (gain) loss		419	83,027	(51,892)
Regulatory assets, Adjustment for Defined Benefit Plan Prior Service Cost		(230)	(230)	(230)
Regulatory asset, Adjustment for Defined Benefit Plan Amortization of Actuarial Loss		(16,372)	(9,823)	(16,744)
Regulatory Asset Adjustment Defined Benefit Plan		(16,183)	72,974	(68,866)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost		8,267	7,213	8,698
Defined Benefit Plan, Interest Cost		18,360	18,198	16,400
Defined Benefit Plan, Expected Return on Plan Assets		(20,676)	(19,496)	(18,721)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		231	223	223
Defined Benefit Plan, Amortization of loss		18,609	10,914	18,294
Defined Benefit Plan Net Periodic Benefit Cost		24,791	17,052	24,894
Defined Benefit Plan Amount Allocated To Construction		(6,834)	(4,625)	(6,712)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	[2]	(8,241)	(4,578)	(9,115)
Defined Benefit Plan Net Amount Charged To Expense		$ 9,716	$ 7,849	$ 9,067
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		3.82%	4.71%	3.84%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.50%	7.50%	7.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate					4.21%	3.85%	4.73%
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		$ 15,696	$ 12,077
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year		16,695
Defined Benefit Plan, Benefits Paid		$ 35,923	$ 19,932	$ 18,855
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 21,589
Defined Benefit Plan, Expected Future Benefit Payments, Year Two					22,028
Defined Benefit Plan, Expected Future Benefit Payments, Year Three					22,974
Defined Benefit Plan, Expected Future Benefit Payments, Year Four					23,950
Defined Benefit Plan, Expected Future Benefit Payments, Year Five					26,242
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter					$ 134,736
Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase		3.25%	3.25%	3.25%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Increase					3.25%	3.25%	3.25%
Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase		5.00%	5.00%	5.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Increase					4.50%	5.00%	5.00%
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		$ 32,072	$ 28,754	$ 28,754	$ 31,049	$ 32,072	$ 28,754
Defined Benefit Plan, Fair Value of Plan Assets		0	0	0	0	0	$ 0
Defined Benefit Plan, Funded Status of Plan					$ (31,049)	$ (32,072)
Reconciliation of change in benefit obligation
Obligation at beginning of period		32,072	28,754
Defined Benefit Plan, Service Cost		527	483	656
Defined Benefit Plan, Interest Cost		1,179	1,252	1,157
Defined Benefit Plan, Plan Amendments	[1]	(3,435)	0
Defined Benefit Plan, Actuarial Loss		2,724	3,454
Defined Benefit Plan, Benefits Paid		2,018	1,871	1,895
Obligation and end of period		31,049	32,072	28,754
Reconciliation of change in plan assets
Fair value of plan assets, beginning of period		0	0
Defined Benefit Plan, Actual Return on Plan Assets		0	0
Defined Benefit Plan, Contributions by Employer		2,018	1,871
Defined Benefit Plan, Benefits Paid		2,018	1,871	1,895
Fair value of plan assets, end of period		0	0	0
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Regulatory assets defined benefit pension actuarial (gain) loss		2,724	3,454	(4,283)
Regulatory assets, Adjustment for Defined Benefit Plan Prior Service Cost		(197)	(197)	(197)
Regulatory asset, Adjustment for Defined Benefit Plan Amortization of Actuarial Loss		(554)	(221)	(733)
Regulatory Asset Adjustment Defined Benefit Plan		1,973	3,036	(5,213)
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Service Cost		527	483	656
Defined Benefit Plan, Interest Cost		1,179	1,252	1,157
Defined Benefit Plan, Expected Return on Plan Assets		0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		197	197	197
Defined Benefit Plan, Amortization of loss		554	221	734
Defined Benefit Plan Net Periodic Benefit Cost		2,457	2,153	2,744
Defined Benefit Plan Amount Allocated To Construction		(808)	(702)	(856)
Defined Benefit Plan Net Amount Deferred To Regulatory Balancing Account	[2]	0	0	0
Defined Benefit Plan Net Amount Charged To Expense		$ 1,649	$ 1,451	$ 1,888
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		3.74%	4.45%	3.56%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate					4.00%	3.74%	4.45%
Pension and Other Postretirement Benefit Contributions [Abstract]
Qualified Defined Benefit Pension Plan Contributions		$ 2,018		$ 1,871
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year		2,035
Defined Benefit Plan, Benefits Paid		2,018	$ 1,871	1,895
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months					$ 2,035
Defined Benefit Plan, Expected Future Benefit Payments, Year Two					2,060
Defined Benefit Plan, Expected Future Benefit Payments, Year Three					2,073
Defined Benefit Plan, Expected Future Benefit Payments, Year Four					2,132
Defined Benefit Plan, Expected Future Benefit Payments, Year Five					2,178
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter					11,068
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		451,200	451,200		411,800	$ 451,200
Defined Benefit Plan, Fair Value of Plan Assets		279,200	279,200		249,300	279,200
Defined Benefit Plan, Funded Status of Plan					(162,500)
Reconciliation of change in benefit obligation
Obligation at beginning of period		451,200
Obligation and end of period		411,800	451,200
Reconciliation of change in plan assets
Fair value of plan assets, beginning of period		279,200
Fair value of plan assets, end of period		249,300	279,200
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax					1	2
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax					11,870	16,604
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax					11,871	16,606
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax		(2,549)	7,221	(3,302)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax		0	7	7
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax		(2,236)	(1,091)	(1,550)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax		(4,785)	6,137	(4,845)
Pension and Other Postretirement Benefit Contributions [Abstract]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year		14,500
Non-Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		36,100	36,100		33,800	$ 36,100
Defined Benefit Plan, Fair Value of Plan Assets		0			0
Reconciliation of change in benefit obligation
Obligation at beginning of period		36,100
Obligation and end of period		33,800	36,100
Reconciliation of change in plan assets
Fair value of plan assets, end of period		0
Defined Benefit Plan Amounts Recognized In Regulatory Amortization And Other Comprehensive Income Net Prior Service Cost Credit Before Tax [Abstract]
Accumulated Other Comprehensive loss, beginning of period		(10,076)	(6,358)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax		2,549	(7,221)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax		0	(7)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax		2,236	1,091
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax		4,785	(6,137)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax, Portion Attributable to Parent		(1,871)	2,419
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax		2,914	(3,718)
Accumulated Other Comprehensive loss, end of period		(7,162)	(10,076)	(6,358)
Western States Office and Professional Employees Union Pension Fund [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Withdrawal Obligation					$ 7,800			$ 8,300
Multiemployer Plans, Withdrawal Payment Per Year For Next 20 Years		600
Multiemployer Plan, Period Contributions		$ 600	$ 400	$ 500
Western States Office and Professional Employees Union Pension Fund [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Collective-Bargaining Arrangement, Percentage of Contributions					4.00%
Western States Office and Professional Employees Union Pension Fund [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Collective-Bargaining Arrangement, Percentage of Contributions					5.00%

[1] We amended our qualified defined benefit pension plan to establish a health retirement account (HRA) plan for participants. The HRA plan permits participants to obtain reimbursement of health care expenses on a nontaxable basis, and the amendment is effective April 1, 2016.

[2] The deferral of defined benefit 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. The balancing account includes the expectation of higher net periodic benefit costs than costs recovered in rates in the near-term with lower net periodic benefit costs than costs recovered in rates expected 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 recognized when amounts are collected in rates. See Note 2.