Regulatory Assets and Liabilities, Regulatory Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory Asset, Current	$ 27,595,000		$ 24,020,000
Regulatory Asset, Noncurrent	290,415,000		324,081,000
Past expenditures not currently earning a return	30,000,000		25,000,000
Pension and Retiree Medical Obligations
Regulatory Assets [Line Items]
Regulatory Asset, Current	17,382,000	[1]	15,038,000	[1]
Regulatory Asset, Noncurrent	200,158,000	[1]	238,398,000	[1]
Regulatory asset, remaining amortization period	Various
Recoverable Deferred Taxes on AFUDC Recorded in Plant
Regulatory Assets [Line Items]
Regulatory Asset, Current	0		0
Regulatory Asset, Noncurrent	31,362,000		27,591,000
Regulatory asset, remaining amortization period	Plant lives
Net AROs
Regulatory Assets [Line Items]
Regulatory Asset, Current	0	[2]	0	[2]
Regulatory Asset, Noncurrent	21,382,000	[2]	21,714,000	[2]
Regulatory asset, remaining amortization period	Plant lives
Conservation Programs
Regulatory Assets [Line Items]
Regulatory Asset, Current	1,951,000	[3]	1,735,000	[3]
Regulatory Asset, Noncurrent	7,753,000	[3]	9,095,000	[3]
Regulatory asset, remaining amortization period, minimum	1 year
Regulatory asset, remaining amortization period, maximum	6 years
Renewable Resources and Environmental Initiatives
Regulatory Assets [Line Items]
Regulatory Asset, Current	3,428,000		4,094,000
Regulatory Asset, Noncurrent	17,671,000		15,101,000
Regulatory asset, remaining amortization period, minimum	1 year
Regulatory asset, remaining amortization period, maximum	4 years
Losses on Reacquired Debt
Regulatory Assets [Line Items]
Regulatory Asset, Current	1,225,000		1,225,000
Regulatory Asset, Noncurrent	3,697,000		4,922,000
Regulatory asset, remaining amortization period	Term of related debt
Deferred Income Tax Adjustment
Regulatory Assets [Line Items]
Regulatory Asset, Current	0		0
Regulatory Asset, Noncurrent	3,375,000		4,859,000
Regulatory asset, remaining amortization period	Typically plant lives
Recoverable Electric Energy Costs
Regulatory Assets [Line Items]
Regulatory Asset, Current	491,000		873,000
Regulatory Asset, Noncurrent	0		0
Regulatory asset, remaining amortization period	Less than one year
Other Regulatory Assets
Regulatory Assets [Line Items]
Regulatory Asset, Current	3,118,000		1,055,000
Regulatory Asset, Noncurrent	$ 5,017,000		$ 2,401,000
Regulatory asset, remaining amortization period	Various

[1] Includes the non-qualified pension plan.

[2] Includes amounts recorded for future recovery of AROs.

[3] Includes costs for conservation programs, as well as incentives allowed in certain jurisdictions.