Fair Value Measurement (Tables)

6 Months Ended

Jun. 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
		June 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	$	111,031		$	111,031	$	—		$	—
International equity		41,948			41,948		—			—
Corporate bonds		48,046			—		48,046			—
US Treasury and government agency securities		55,231			55,231		—			—
Agency mortgage and asset backed securities		15,497			—		15,497			—
Other		11,923			11,923		—			—
Bond, reserve and construction funds		197			197		—			—
Long-term investments:
Corporate bonds		5,995			—		5,995			—
US Treasury and government agency securities		6,889			6,889		—			—
Agency mortgage and asset backed securities		2,670			—		2,670			—
Mutual funds		59,803			59,803		—			—
Interest rate options		39,215			—		—			39,215	(1)
Natural gas swaps		(4,265	)		—		(4,265	)		—

				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 $20,690,000 and $43,070,000 of collateral received by the counterparties at June 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 June 30, 2012
	Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at March 31, 2012	$	66,860
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(27,645	)
Balance at June 30, 2012	$	39,215

		Three Months Ended June 30, 2011
		Decommissioning funds			Long-term investments
		(dollars in thousands)
Assets (Liabilities):
Balance at March 31, 2011	$	(548	)	$	8,408
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		43			40
Liquidations		—			(400	)
Balance at June 30, 2011	$	(505	)	$	8,048

		Six Months Ended June 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			—			(30,231	)
Impairment included in other comprehensive margin (deficit)		—			887			—
Liquidations		—			(8,600	)		—
Balance at June 30, 2012	$	—		$	—		$	39,215

		Six Months Ended June 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)		(53	)		77
Liquidations		—			(700	)
Balance at June 30, 2011	$	(505	)	$	8,048