Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 288,097		$ 278,382		$ 266,907
Current Regulatory Liabilities	24,810		31,046		28,593
Gas Costs Payable [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	596		8,420		1,250
Current Regulatory Liabilities	10,069		17,994		16,991
Unrealized Gain On Derivatives [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	5,608	[1]	0	[1]	227	[1]
Current Regulatory Liabilities	6,771	[1]	2,853	[1]	3,932	[1]
Other Regulatory [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	2,996	[2]	2,607	[2]	2,307	[2]
Current Regulatory Liabilities	7,970	[2]	10,199	[2]	7,670	[2]
Accrued Asset Removal Costs [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 278,897		$ 267,355		$ 263,123

[1] Unrealized gains or losses on derivatives are non-cash items and therefore do not earn a rate of return or a carrying charge. These amounts are recoverable through utility rates as part of the annual Purchased Gas Adjustment mechanism when realized at settlement.

[2] Other primarily consists of deferrals and amortizations under other approved regulatory mechanisms. The accounts being amortized typically earn a rate of return or carrying charge.