Fair Value (Tables)

9 Months Ended

Sep. 30, 2016

Fair Value

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

	Fair Value Measurements at Reporting Date Using
		September 30, 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	$	163,202	$	163,202	$	—	$	—
International equity trust		70,475		—		70,475		—
Corporate bonds		48,943		—		48,943		—
US Treasury and government agency securities		72,798		72,798		—		—
Agency mortgage and asset backed securities		22,395		—		22,395		—
Municipal bonds		404		—		404		—
Other		7,988		7,988		—		—
Long-term investments:
International equity trust		15,573		—		15,573		—
Corporate bonds		11,395		—		11,395		—
US Treasury and government agency securities		13,037		13,037		—		—
Agency mortgage and asset backed securities		1,825		—		1,825		—
Mutual funds		57,462		57,462		—		—
Other		409		409		—		—
Interest rate options		—		—		—		—
Natural gas swaps		2,823		—		2,823		—

	Fair Value Measurements at Reporting Date Using
		December 31, 2015		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	$	151,178	$	151,178	$	—	$	—
International equity trust		68,753		—		68,753		—
Corporate bonds		48,450		—		48,450		—
US Treasury and government agency securities		75,173		74,698		475		—
Agency mortgage and asset backed securities		15,503		—		15,503		—
Other		4,772		4,772		—		—
Long-term investments:
Corporate bonds		9,903		—		9,903		—
US Treasury and government agency securities		13,772		13,772		—		—
Agency mortgage and asset backed securities		1,121		—		1,121		—
International equity trust		12,846		—		12,846		—
Mutual funds		48,649		48,649		—		—
Other		479		479		—		—
Interest rate options		1,010		—		—		1,010
Natural gas swaps		24,995		—		24,995		—

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

		Three Months Ended September 30, 2016
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at June 30, 2016	$	5
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(5	)
Balance at September 30, 2016	$	—

		Three Months Ended September 30, 2015
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at June 30, 2015	$	4,715
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(3,213	)
Balance at September 30, 2015	$	1,502

		Nine Months Ended September 30, 2016
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2015	$	1,010
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(1,010	)
Balance at September 30, 2016	$	—

		Nine Months Ended September 30, 2015
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2014	$	4,371
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(2,869	)
Balance at September 30, 2015	$	1,502

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 September 30, 2016 and December 31, 2015 were as follows (in thousands):

		2016				2015
		Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt	$	8,136,564	$	9,752,299	$	7,575,027	$	8,445,630