Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Regulatory Liabilities [Line Items]
Regulatory liabilities		$ 328,646	$ 317,205	$ 309,327
Current Regulatory Liabilities		26,712	19,105	26,742
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities		3,615	2,507	1,057
Current Regulatory Liabilities		20,087	5,700	6,423
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	[1]	1,369	0	1,202
Current Regulatory Liabilities	[1]	1,015	240	11,286
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	[2]	3,456	3,460	3,501
Current Regulatory Liabilities	[2]	5,610	13,165	9,033
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	[3]	$ 320,206	$ 311,238	$ 303,567

[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 Note 2 of the 2014 Form 10-K.