Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 298,220		$ 288,113		$ 288,097
Current Regulatory Liabilities	16,506		20,792		24,810
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	11		0		596
Current Regulatory Liabilities	3,096		9,100		10,069
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,682	[1]	3,639	[1]	5,608	[1]
Current Regulatory Liabilities	1,386	[1]	1,950	[1]	6,771	[1]
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3,522	[2]	3,261	[2]	2,996	[2]
Current Regulatory Liabilities	12,024	[2]	9,742	[2]	7,970	[2]
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 293,005		$ 281,213		$ 278,897

[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.