Risk Management and Derivative Instruments - Gross Fair Value of Derivative Instruments by Appropriate Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	May 04, 2017
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Net recorded fair value	$ 5,879	$ 18,813	$ 51,329
Asset Derivatives, Net recorded fair value	6,364	2,469	$ 33,800
Liability Derivatives, Net recorded fair value	253	139
Liability Derivatives, Net recorded fair value	305	0
Short-Term Derivative Instruments [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	11,766	21,217
Asset Derivatives, Netting arrangements	(5,887)	(2,404)
Asset Derivatives, Net recorded fair value	5,879	18,813
Liability Derivatives, Gross fair value	6,140	2,543
Liability Derivatives, Netting arrangements	(5,887)	(2,404)
Liability Derivatives, Net recorded fair value	253	139
Short-Term Derivative Instruments [Member] \| Commodity derivatives [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	11,518	21,217
Liability Derivatives, Gross fair value	5,887	2,543
Short-Term Derivative Instruments [Member] \| Interest Rate Swaps [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	248	0
Liability Derivatives, Gross fair value	253	0
Long-Term Derivative Instruments [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	7,337	4,298
Asset Derivatives, Netting arrangements	(973)	(1,829)
Asset Derivatives, Net recorded fair value	6,364	2,469
Liability Derivatives, Gross fair value	1,278	1,829
Liability Derivatives, Netting arrangements	(973)	(1,829)
Liability Derivatives, Net recorded fair value	305	0
Long-Term Derivative Instruments [Member] \| Commodity derivatives [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	6,990	4,298
Liability Derivatives, Gross fair value	973	1,829
Long-Term Derivative Instruments [Member] \| Interest Rate Swaps [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Gross fair value	347	0
Liability Derivatives, Gross fair value	$ 305	$ 0

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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