Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Regulatory Liabilities [Line Items]
Current Regulatory Liabilities	$ 19,105		$ 28,335
Regulatory liabilities	317,205		303,485
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Current Regulatory Liabilities	5,700		7,510
Regulatory liabilities	2,507		2,172
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Current Regulatory Liabilities	240	[1]	5,290	[1]
Regulatory liabilities	0	[1]	1,880	[1]
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Current Regulatory Liabilities	13,165	[2]	15,535	[2]
Regulatory liabilities	3,460	[2]	3,139	[2]
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 311,238	[3]	$ 296,294	[3]

[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

[3] Estimated costs of removal on certain regulated properties are collected through rates. See "Accounting Policies—Plant, Property, and Accrued Asset Removal Costs" below.