Regulatory Assets and Liabilities, Regulatory Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory Asset, Current	$ 14,866,000		$ 12,048,000
Regulatory Asset, Noncurrent	233,193,000		240,459,000
Past expenditures not currently earning a return	100,000		400,000
Environmental Remediation Costs
Regulatory Assets [Line Items]
Regulatory Asset, Current	4,376,000		2,521,000
Regulatory Asset, Noncurrent	117,684,000		109,162,000
Regulatory asset, remaining amortization period	Various
Pension and Retiree Medical Obligations
Regulatory Assets [Line Items]
Regulatory Asset, Current	8,202,000	[1]	7,328,000	[1]
Regulatory Asset, Noncurrent	85,220,000	[1]	104,426,000	[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	12,679,000		10,458,000
Regulatory asset, remaining amortization period	Plant lives
Losses on Reacquired Debt
Regulatory Assets [Line Items]
Regulatory Asset, Current	801,000		800,000
Regulatory Asset, Noncurrent	5,737,000		6,538,000
Regulatory asset, remaining amortization period	Term of related debt
State Commission Adjustments
Regulatory Assets [Line Items]
Regulatory Asset, Current	410,000		339,000
Regulatory Asset, Noncurrent	9,355,000		7,533,000
Regulatory asset, remaining amortization period	Plant lives
Conservation Programs
Regulatory Assets [Line Items]
Regulatory Asset, Current	404,000		691,000
Regulatory Asset, Noncurrent	0		0
Regulatory asset, remaining amortization period	Less than one year
Deferred Income Tax Adjustment
Regulatory Assets [Line Items]
Regulatory Asset, Current	0		0
Regulatory Asset, Noncurrent	1,763,000		1,974,000
Regulatory asset, remaining amortization period	Typically plant lives
Recoverable Purchased Natural Gas And Electric Energy Costs
Regulatory Assets [Line Items]
Regulatory Asset, Current	673,000		358,000
Regulatory Asset, Noncurrent	0		0
Regulatory asset, remaining amortization period	Less than one year
Other Regulatory Assets
Regulatory Assets [Line Items]
Regulatory Asset, Current	0		11,000
Regulatory Asset, Noncurrent	$ 755,000		$ 368,000
Regulatory asset, remaining amortization period	Various

[1] Includes the non-qualified pension plan.