Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 309,327		$ 303,485		$ 294,202
Current Regulatory Liabilities	26,742		28,335		16,644
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,057		2,172		481
Current Regulatory Liabilities	6,423		7,510		6,353
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,202	[1]	1,880	[1]	1,054	[1]
Current Regulatory Liabilities	11,286	[1]	5,290	[1]	547	[1]
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3,501	[2]	3,139	[2]	3,562	[2]
Current Regulatory Liabilities	9,033	[2]	15,535	[2]	9,744	[2]
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 303,567		$ 296,294		$ 289,105

[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.