Fair Value of Financial Assets and Liabilities (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value of Financial Assets and Liabilities [Abstract]

Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Loss

Financial Impact of Qualifying Cash Flow Hedges — The impact of qualifying interest rate cash flow hedges on SPS' accumulated other comprehensive loss, included as a component of common stockholder's equity and in the statement of comprehensive income, is detailed in the following table:

	Three Months Ended March 31
(Thousands of Dollars)	2013				2012
Accumulated other comprehensive loss related to cash flow hedges at Jan. 1		$	(1,332	)		$	(1,504	)
After-tax net realized losses on derivative transactions reclassified into earnings			42				43
Accumulated other comprehensive loss related to cash flow hedges at March 31		$	(1,290	)		$	(1,461	)

Carrying Amount and Fair Value of Long-term Debt

As of March 31, 2013 and Dec. 31, 2012, other financial instruments for which the carrying amount did not equal fair value were as follows:

	March 31, 2013				Dec. 31, 2012
	Carrying				Carrying
(Thousands of Dollars)	Amount		Fair Value		Amount		Fair Value
Long-term debt, including current portion	$	1,103,740	$	1,317,029	$	1,103,684	$	1,327,538