Cost and Fair Value Basis of Long-Term Debt (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Long Term Debt By Maturity Abstract
Short-term debt	$ 113,700	$ 141,600	$ 186,435
Long Term Debt Maturities Repayment Terms	Our utility’s long-term debt consists of secured Medium Term Notes (MTNs) with maturity dates ranging from 2014 through 2035, interest rates ranging from 3.176 percent to 9.05 percent, and a weighted-average coupon rate of 5.85 percent. During the three months ended March 31, 2012, we redeemed $40 million of MTNs. Our gas storage segment’s long-term debt consists of $40 million of fixed and variable senior secured notes with a maturity date of November 30, 2016. The $20 million fixed portion of the debt has an interest rate of 7.75 percent, and the $20 million variable portion currently has an interest rate of 7.00 percent. See Note 7 in our 2011 Form 10-K for more detail on long-term debt.
Mediumterm Notes Abstract
Carrying Amount	641,700	681,700	601,700
Estimated Fair Value	$ 742,852	$ 808,724	$ 680,436

Disclosure of timing of required repayments, sinking fund requirements, and other redeemable securities at fixed or determinable prices and dates in the five years immediately following the date of the latest balance sheet presented in the financial statements, and the amount thereafter to fully repay the principal of long-term debt. These disclosures may be made either on an individual debt or security basis, by type of debt or security basis, or on a combined basis.

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Including the current and noncurrent portions, carrying value at the balance sheet date of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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