Fair Value (Tables)

6 Months Ended

Jun. 30, 2017

Fair Value

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

	Fair Value Measurements at Reporting Date Using
		June 30, 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	$	132,230	$	132,230	$	—	$	—
International equity trust		77,338		—		77,338		—
Corporate bonds		66,221		—		66,221		—
US Treasury and government agency securities		74,414		74,414		—		—
Agency mortgage and asset backed securities		14,743		—		14,743		—
Mutual funds		45,353		45,353		—		—
Municipal bonds		471		—		471		—
Other		3,360		3,360		—		—
Long-term investments:
International equity trust		19,707		—		19,707		—
Corporate bonds		14,025		—		14,025		—
US Treasury and government agency securities		12,134		12,134		—		—
Agency mortgage and asset backed securities		1,344		—		1,344		—
Mutual funds		71,098		71,098		—		—
Other		351		351		—		—
Natural gas swaps		858		—		858		—

	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 June 30, 2017 and December 31, 2016 were as follows (in thousands):

		2017				2016
		Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt	$	8,101,124	$	8,973,180	$	8,304,523	$	9,043,029