Summary of Significant Accounting Policies Regulatory Liabilities Disclosure (details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 308,858		$ 303,485		$ 293,135
Current Regulatory Liabilities	37,686		28,335		28,239
Gas Costs Payable [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	2,602		2,172		1,407
Current Regulatory Liabilities	9,137		7,510		8,694
Unrealized Gain On Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,078	[1]	1,880	[1]	2,836	[1]
Current Regulatory Liabilities	15,788	[1]	5,290	[1]	8,054	[1]
Other Regulatory [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	6,152	[2]	3,139	[2]	3,455	[2]
Current Regulatory Liabilities	12,761	[2]	15,535	[2]	11,491	[2]
Accrued Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 299,026		$ 296,294		$ 285,437

[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 deferrals and amortizations under other approved regulatory mechanisms. The accounts being amortized typically earn a rate of return or carrying charge.