Fair Value (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value

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
	June 30, 2019		(Level 1)		(Level 2)		(Level 3)
	(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	161,570	$	161,570	$	—	$	—
International equity trust		90,317		—		90,317		—
Corporate bonds and debt		60,809		—		60,809		—
US Treasury securities		51,422		51,422		—		—
Mortgage backed securities		54,478		—		54,478		—
Domestic mutual funds		51,820		51,820		—		—
Municipal bonds		316		—		316		—
Federal agency securities		2,541		—		2,541		—
Non-US Gov't bonds & private placements		265		—		265		—
Other		5,438		5,438		—		—
Long-term investments:
International equity trust		21,734		—		21,734		—
Corporate bonds and debt		15,861		—		15,861		—
US Treasury securities		12,792		12,792		—		—
Mortgage backed securities		9,867		—		9,867		—
Domestic mutual funds		89,879		89,879		—		—
Federal agency securities		767		—		767		—
Treasury STRIPS		36,043		—		36,043		—
Other		2,411		2,411		—		—
Natural gas swaps		23,000		—		23,000		—

	Fair Value Measurements at Reporting Date Using
			Quoted Prices in		Significant Other		Significant
			Active Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
	December 31, 2018		(Level 1)		(Level 2)		(Level 3)
	(dollars in thousands)
Nuclear decommissioning trust funds:
Domestic equity	$	136,196	$	136,196	$	—	$	—
International equity trust		76,852		—		76,852		—
Corporate bonds and debt		51,356		—		48,853		2,503
US Treasury securities		47,712		47,712		—		—
Mortgage backed securities		56,004		—		56,004		—
Domestic mutual funds		43,359		43,359		—		—
Municipal bonds		278		—		278		—
Federal agency securities		6,066		—		6,066		—
Non-US Gov't bonds & private placements		964		—		964		—
Other		2,031		2,031		—		—
Long-term investments:
International equity trust		17,382		—		17,382		—
Corporate bonds and debt		12,571		—		11,366		1,205
US Treasury securities		12,062		12,062		—		—
Mortgage backed securities		11,517		—		11,517		—
Domestic mutual funds		94,494		94,494		—		—
Federal agency securities		941		—		941		—
Treasury STRIPS		14,113		—		14,113		—
Other		1,045		1,045		—		—
Natural gas swaps		13,154		—		13,154		—

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

	Three Months Ended
	June 30, 2019
Assets (Liabilities):	Corporate bonds and debt
	(dollars in thousands)
Balance at March 31, 2019	$	1,317
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		8
Liquidations		(1,325)
Balance at June 30, 2019	$	—

	Six Months Ended
	June 30, 2019
Assets (Liabilities):	Corporate bonds and debt
	(dollars in thousands)
Balance at December 31, 2018	$	3,708
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		94
Liquidations		(3,802)
Balance at June 30, 2019	$	—

	Three Months Ended
	June 30, 2018
Assets (Liabilities):	Corporate bonds and debt
	(dollars in thousands)
Balance at March 31, 2018	$	3,807
Transfers to Level 3		1,190
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		—
Balance at June 30, 2018	$	4,997

	Six Months Ended
	June 30, 2018
Assets (Liabilities):	Corporate bonds and debt
	(dollars in thousands)
Balance at December 31, 2017	$	—
Transfers to Level 3		4,997
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		—
Balance at June 30, 2018	$	4,997

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, 2019 and December 31, 2018 were as follows (in thousands):

	2019				2018
	Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt	$	9,213,008	$	10,522,766	$	9,347,307	$	9,837,254