Summary of Significant Accounting Policies (details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounting Policies Abstract
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.80%	2.80%	2.90%
Weighted Average Depreciation Rates Transmission Distribution	2.70%
Weighted Average Depreciation Rates Utility Storage	2.20%
Weighted Average Depreciation Rates General Plant	4.60%
Weighted Average Depreciation Rates Intangible Other	5.10%
Public Utilities, Allowance for Funds Used During Construction, Additions	0.50%	0.60%	1.00%
Outstanding Checks In Accounts Payable	$ 3,900,000
Unbilled Receivables, Current	61,925,000	64,803,000
Senate Bill Four Zero Eight Charge	7,400,000
Inventory - Gas	65,600,000	70,700,000
Inventory - Materials and supplies	8,800,000	9,700,000
Deferred Tax Liabilities, Deferred Expense	68,500,000	72,300,000
Table Of Regulatory Assets [Abstract]
Current Regulatory Assets	94,673,000	52,714,000
Regulatory Assets	371,392,000	348,897,000
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	31,046,000	17,828,000
Regulatory Liabilities	278,382,000	258,031,000
Gas Costs Payable [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	17,994,000	15,583,000
Regulatory Liabilities	8,420,000	2,297,000
Unrealized Gain On Derivatives [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	2,853,000	2,245,000
Regulatory Liabilities	0	628,000
Other Regulatory [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	10,199,000	0
Regulatory Liabilities	2,607,000	2,165,000
Accrued Asset Removal Costs [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory Liabilities	267,355,000	252,941,000
Unrealized Loss On Derivatives [Member]
Table Of Regulatory Assets [Abstract]
Current Regulatory Assets	57,317,000	38,437,000
Regulatory Assets	6,536,000	17,022,000
Pension and Other Postretirement Benefit Liabilities [Member]
Table Of Regulatory Assets [Abstract]
Current Regulatory Assets	15,491,000	10,988,000
Regulatory Assets	170,512,000	118,248,000
Other Regulatory [Member]
Table Of Regulatory Assets [Abstract]
Current Regulatory Assets	21,865,000	3,289,000
Regulatory Assets	23,410,000	26,975,000
Income Tax Asset [Member]
Table Of Regulatory Assets [Abstract]
Regulatory Assets	65,264,000	72,341,000
Environmental Costs [Member]
Table Of Regulatory Assets [Abstract]
Regulatory Assets	$ 105,670,000	$ 114,311,000