Fair Value (Tables)

3 Months Ended

Mar. 31, 2017

Fair Value

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

	Fair Value Measurements at Reporting Date Using
		March 31, 2017			Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
		(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	128,483		$	128,483	$	—		$	—
International equity trust		70,815			—		70,815			—
Corporate bonds		67,336			—		67,336			—
US Treasury and government agency securities		68,026			68,026		—			—
Agency mortgage and asset backed securities		18,157			—		18,157			—
Mutual funds		44,172			44,172		—			—
Municipal bonds		313			—		313			—
Other		2,720			2,720		—			—
Long-term investments:
International equity trust		16,895			—		16,895			—
Corporate bonds		14,145			—		14,145			—
US Treasury and government agency securities		11,849			11,849		—			—
Agency mortgage and asset backed securities		1,386			—		1,386			—
Mutual funds		62,169			62,169		—			—
Natural gas swaps		(4,968	)		—		(4,968	)		—

	Fair Value Measurements at Reporting Date Using
		December 31, 2016			Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
		(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	170,408		$	170,408	$	—		$	—
International equity trust		66,861			—		66,861			—
Corporate bonds		60,019			—		60,019			—
US Treasury and government agency securities		65,725			65,725		—			—
Agency mortgage and asset backed securities		17,410			—		17,410			—
Municipal bonds		943			—		943
Other		4,663			4,663		—			—
Long-term investments:
Corporate bonds		11,853			—		11,853			—
US Treasury and government agency securities		12,187			12,187		—			—
Agency mortgage and asset backed securities		1,651			—		1,651			—
International equity trust		15,946			—		15,946			—
Mutual funds		57,932			57,932		—			—
Other		305			305		—			—
Natural gas swaps		(15,090	)		—		(15,090	)		—

Schedule of estimated fair values of long-term debt, including current maturities

The estimated fair values of our long-term debt, including current maturities at March 31, 2017 and December 31, 2016 were as follows (in thousands):

		2017				2016
		Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt	$	8,123,581	$	8,858,128	$	8,304,523	$	9,043,029