Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	$ 20,792	$ 31,046
Regulatory liabilities	288,113	278,382
Gas Costs Payable [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	9,100	17,994
Regulatory liabilities	0	8,420
Unrealized Gain On Derivatives [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	1,950	2,853	[1]
Regulatory liabilities	3,639	0	[1]
Other Regulatory [Member]
Table Of Regulatory Liabilities [Abstract]
Current Regulatory Liabilities	9,742	10,199	[2]
Regulatory liabilities	3,261	2,607	[2]
Accrued Asset Removal Costs [Member]
Table Of Regulatory Liabilities [Abstract]
Regulatory liabilities	$ 281,213	$ 267,355

[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 (PGA) mechanism when realized at settlement.

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