Derivative Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Summary of Open Commodity Derivative Contracts

Year	Index	Total Volumes		Weighted Average Price per Unit			Fair Value - June 30, 2018
		(in millions)					Asset (Liability)
Natural gas fixed price swaps		(Mmbtu)		($/Mmbtu)
2018 (July through December)	NYMEX-Henry Hub		141.1	$	2.89		$	(9,430	)
2019	NYMEX-Henry Hub		167.3	$	2.85			(4,557	)
2020	NYMEX-Henry Hub		15.5	$	2.76			(2,662	)
Natural gas basis swaps (1)		(Mmbtu)		($/Mmbtu)
2018 (July through December)	NW Rockies Basis Swap		94.6	$	(0.68	)	$	(3,176	)
2019	NW Rockies Basis Swap		84.5	$	(0.70	)		(848	)
2020	NW Rockies Basis Swap		—	$	—			—
Crude oil fixed price swaps		(Bbl)		($/Bbl)
2018 (July through December)	NYMEX-WTI	1.2		$	60.53		$	(12,050	)
2019	NYMEX-WTI	1.7		$	58.83			(11,645	)
2020	NYMEX-WTI	.09		$	60.05			(204	)

⁽¹⁾ Represents swap contracts that fix the basis differentials for gas sold at or near Opal, Wyoming and the value of natural gas established on the last trading day of the month by the NYMEX for natural gas swaps for the respective period.

Subsequent to June 30, 2018 and through July 24, 2018, the Company has entered into the following open commodity derivative contracts to manage commodity price risk.

Type	Index	Total Volumes	Weighted Average Price per Unit
		(in millions)
Natural gas basis swaps (1)		(Mmbtu)	($/Mmbtu)
2018 (August through October)	NYMEX-Henry Hub	6.4	$	(0.48	)

⁽¹⁾ Represents swap contracts that fix the basis differentials for gas sold at or near Opal, Wyoming and the value of natural gas established on the last trading day of the month by the NYMEX for natural gas swaps for the respective period.

Summary of Pre-tax Realized and Unrealized Gain (Loss) Recognized Related to Derivative Instruments

	For the Quarter Ended						For the Six Months
	Ended June 30,						Ended June 30,
Commodity Derivatives:	2018			2017			2018			2017
Realized gain (loss) on commodity derivatives - natural gas (1)	$	10,982		$	(868	)	$	12,426		$	(868	)
Realized loss on commodity derivatives - oil (1)		(4,320	)		—			(4,690	)		—
Unrealized gain (loss) on commodity derivatives (1)		(53,933	)		21,585			(61,539	)		8,367
Total gain (loss) on commodity derivatives	$	(47,271	)	$	20,717		$	(53,803	)	$	7,499

⁽¹⁾ Included in (Loss) gain on commodity derivatives in the Consolidated Statements of Operations.