Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Measurement

Schedule of assets and liabilities measured at fair value on a recurring basis

				Fair Value Measurements at Reporting Date Using
		September 30, 2012			Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
		(dollars in thousands)
Decommissioning funds:
Domestic equity	$	117,995		$	117,995	$	—		$	—
International equity		45,610			45,610		—			—
Corporate bonds		51,269			—		51,269			—
US Treasury and government agency securities		49,638			49,638		—			—
Agency mortgage and asset backed securities		25,725			—		25,725			—
Other		6,386			6,386		—			—
Bond, reserve and construction funds		197			197		—			—
Long-term investments:
Corporate bonds		6,076			6,076		—			—
US Treasury and government agency securities		6,811			6,811		—			—
Agency mortgage and asset backed securities		2,828			2,828		—			—
Mutual funds		59,970			59,970		—			—
Other		225			225		—			—
Interest rate options		29,921			—		—			29,921	(1)
Natural gas swaps		(13	)		—		(13	)		—

				Fair Value Measurements at Reporting Date Using
		December 31, 2011			Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
		(dollars in thousands)
Decommissioning funds:
Domestic equity	$	102,285		$	102,285	$	—		$	—
International equity		39,618			39,618		—			—
Corporate bonds		41,338			—		41,338			—
US Treasury and government agency securities		41,697			41,697		—			—
Agency mortgage and asset backed securities		28,519			—		28,519			—
Derivative instruments		(982	)		—		—			(982	)
Other		16,122			16,122		—			—
Bond, reserve and construction funds		2,720			2,720		—			—
Long-term investments		80,055			72,342		—			7,713	(2)
Interest rate options		69,446			—		—			69,446	(1)
Natural gas swaps		(7,220	)		—		(7,220	)		—

⁽¹⁾

Interest rate options as reflected on the unaudited condensed Balance Sheet includes the fair value of the interest rate options offset by $7,810,000 and $43,070,000 of collateral received by the counterparties at September 30, 2012 and December 31, 2011, respectively.

⁽²⁾

Represents auction rate securities investments we held.

Schedule of changes in Level 3 assets and liabilities measured at fair value on a recurring basis

		Three Months Ended September 30, 2012
	Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at June 30, 2012	$	39,215
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(9,294	)
Balance at September 30, 2012	$	29,921

		Three Months Ended September 30, 2011
		Decommissioning funds			Long-term investments
		(dollars in thousands)
Assets (Liabilities):
Balance at June 30, 2011	$	(505	)	$	8,048
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(527	)
Impairment included in other comprehensive deficit					50
Liquidations					(400	)
Balance at September 30, 2011	$	(1,032	)	$	7,698

		Nine Months Ended September 30, 2012
		Decommissioning funds			Long-term investments			Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2011	$	(982	)	$	7,713		$	69,446
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		982			—			(39,525	)
Impairment included in other comprehensive margin (deficit)		—			887			—
Liquidations		—			(8,600	)		—
Balance at September 30, 2012	$	—		$	—		$	29,921

		Nine Months Ended September 30, 2011
		Decommissioning funds			Long-term investments
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2010	$	(452	)	$	8,671
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(580	)		127
Liquidations		—			(1,100	)
Balance at September 30, 2011	$	(1,032	)	$	7,698