Derivative Instruments (Tables)

6 Months Ended

Jun. 30, 2016

Derivative Instruments

Schedule of volume activity of natural gas derivatives that is expected to settle or mature each year

Year	Natural Gas Swaps (MMBTUs) (in millions)
2016	15.1
2017	19.3
2018	16.5
2019	11.4
2020	5.5
Total	67.8

Schedule of remaining notional amount of forecasted debt issuances hedged in each year with LIBOR swaptions

Year		LIBOR Swaption Notional Dollar Amount (in thousands)
2016	$	157,865
2017		80,169
Total	$	238,034

Schedule of fair value of derivative instruments and their effect on consolidated balance sheets

	Balance Sheet Location		Fair Value
			2016			2015
			(dollars in thousands)
Assets:
Interest rate options	Other deferred charges	$	5		$	1,010
Natural gas swaps	Other deferred charges	$	4,982		$	—
Liabilities:
Natural gas swaps	Other current liabilities	$	(2,337	)	$	22,848

Schedule of the gross realized gains and (losses) on derivative instruments recognized in margin

	Statement of Revenues and Expenses		Three months ended June 30,					Six months ended June 30,
	Location		2016			2015		2016			2015
			(dollars in thousands)
Natural Gas Swaps	Fuel	$	7		$	956	$	18		$	1,236
Natural Gas Swaps	Fuel		(8,111	)		—		(12,339	)		—
		$	(8,104	)	$	956	$	(12,321	)	$	1,236

Schedule of unrealized gains and (losses) on derivative instruments deferred on the balance sheet

	Balance Sheet Location		2016			2015
			(dollars in thousands)
Natural gas swaps	Regulatory liability	$	2,645		$	—
Natural gas swaps	Regulatory asset		—			(22,848	)
Interest rate options	Regulatory asset		(16,901	)		(25,915	)
Total unrealized gains (losses)		$	(14,256	)	$	(48,763	)

Schedule of gross amounts of derivatives and their related offset amounts as permitted by their respective master netting agreements and obligations to return cash collateral

		Gross Amounts of Recognized Assets (Liabilities)			Gross Amounts offset on the Balance Sheet			Cash Collateral		Net Amounts of Assets Presented on the Balance Sheet
		(dollars in thousands)
June 30, 2016
Assets:
Natural gas swaps	$	2,645		$	—		$	—	$	2,645
Interest rate options	$	16,906		$	(16,901	)	$	—	$	5
December 31, 2015
Assets:
Natural gas swaps	$	(22,848	)	$	—		$	—	$	(22,848	)
Interest rate options	$	26,925		$	(25,915	)	$	—	$	1,010