Fair Value (Tables)

9 Months Ended

Sep. 30, 2018

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



	Fair Value Measurements at Reporting Date Using

			Quoted Prices in		Significant Other		Significant
			Active Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
	September 30, 2018		(Level 1)		(Level 2)		(Level 3)
	(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	157,382	$	157,382	$	—	$	—
International equity trust		87,462		—		87,462		—
Corporate bonds and debt		59,134		—		56,276		2,858
US Treasury securities		35,578		35,578		—		—
Mortgage backed securities		58,788		—		58,788		—
Domestic mutual funds		52,994		52,994		—		—
Municipal bonds		283		—		283		—
Federal agency securities		6,832		—		6,832		—
Non-US Gov't bonds & private placements		1,119		—		1,119		—
Other		1,402		1,402		—		—
Long-term investments:
International equity trust		19,776		—		19,776		—
Corporate bonds and debt		15,018		—		13,535		1,483
US Treasury securities		8,084		8,084		—		—
Mortgage backed securities		12,410		—		12,410		—
Domestic mutual funds		100,175		100,175		—		—
Federal agency securities		1,002		—		1,002		—
Treasury STRIPS		9,223		—		9,223		—
Other		118		118		—		—
Natural gas swaps		14,961		—		14,961		—



	Fair Value Measurements at Reporting Date Using

			Quoted Prices in		Significant Other		Significant Other
			Active Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
	December 31, 2017		(Level 1)		(Level 2)		(Level 3)
	(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	142,419	$	142,419	$	—	$	—
International equity trust		88,820		—		88,820		—
Corporate bonds and debt		66,317		—		66,317		—
US Treasury securities		38,791		38,791		—		—
Mortgage backed securities		49,379		—		49,379		—
Domestic mutual funds		47,833		47,833		—		—
Municipal bonds		92		—		92		—
Federal agency securities		3,725		—		3,725		—
Other		7,679		7,679		—		—
Long-term investments:
International equity trust		20,071		—		20,071		—
Corporate bonds and debt		16,215		—		16,215		—
US Treasury securities		6,670		6,670		—		—
Mortgage backed securities		7,267		—		7,267		—
Domestic mutual funds		87,011		87,011		—		—
Federal agency securities		259		—		259		—
Other		3,129		3,129		—		—
Natural gas swaps		6,328		—		6,328		—

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



	Three Months Ended
	September 30, 2018

	Corporate bonds and debt
	(dollars in thousands)
Balance at June 30, 2018	$	4,997
Transfers from Level 3		—
Total gains or losses (realized/unrealized):
Changes in net assets		(656)
Balance at September 30, 2018	$	4,341



	Nine Months Ended
	September 30, 2018

	Corporate bonds and debt
	(dollars in thousands)
Balance at December 31, 2017	$	—
Transfers to Level 3		4,997
Total gains or losses (realized/unrealized):
Changes in net assets		(656)
Balance at September 30, 2018	$	4,341

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, 2018 and December 31, 2017 were as follows (in thousands):



	2018				2017
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
	(in thousands)
Long-term debt	$	8,936,098	$	9,235,718	$	8,232,703	$	9,155,942