Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 312,500		$ 303,485		$ 298,220
Current Regulatory Liabilities	23,352		28,335		16,506
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	410		2,172		11
Current Regulatory Liabilities	6,704		7,510		3,096
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	602	[1]	1,880	[1]	1,682	[1]
Current Regulatory Liabilities	5,320	[1]	5,290	[1]	1,386	[1]
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3,673	[2]	3,139	[2]	3,522	[2]
Current Regulatory Liabilities	11,328	[2]	15,535	[2]	12,024	[2]
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 307,815		$ 296,294		$ 293,005

[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] These balances primarily consist of deferrals and amortizations under approved regulatory mechanisms. The accounts being amortized typically earn a rate of return or carrying charge.