Fair Value of Financial Assets and Liabilities (Tables)

9 Months Ended

Sep. 30, 2012

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 Sept. 30
(Thousands of Dollars)	2012				2011
Accumulated other comprehensive loss related to cash flow hedges at July 1		$	(1,418	)		$	(1,589	)
After-tax net realized losses on derivative transactions reclassified into earnings			43				42
Accumulated other comprehensive loss related to cash flow hedges at Sept. 30		$	(1,375	)		$	(1,547	)

	Nine Months Ended Sept. 30
(Thousands of Dollars)	2012				2011
Accumulated other comprehensive loss related to cash flow hedges at Jan. 1		$	(1,504	)		$	(1,675	)
After-tax net realized losses on derivative transactions reclassified into earnings			129				128
Accumulated other comprehensive loss related to cash flow hedges at Sept. 30		$	(1,375	)		$	(1,547	)

Carrying Amount and Fair Value of Long-term Debt

As of Sept. 30, 2012 and Dec. 31, 2011, other financial instruments for which the carrying amount did not equal fair value were as follows:

	Sept. 30, 2012				Dec. 31, 2011
	Carrying				Carrying
(Thousands of Dollars)	Amount		Fair Value		Amount		Fair Value
Long-term debt, including current portion	$	1,103,625	$	1,341,654	$	993,314	$	1,176,020