Risk Management and Derivative Instruments - Gross Fair Value of Derivative Instruments by Appropriate Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Derivative Instruments and Hedges, Assets [Abstract]
Asset Derivatives, Net recorded fair value	$ 1,522	$ 873
Liability Derivatives, Net recorded fair value	30,391	10,824
Liability Derivatives, Net recorded fair value	5,355	847
Short-Term Derivative Instruments [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	2,547	6,088
Asset Derivatives, Netting arrangements	(2,547)	(6,088)
Asset Derivatives, Net recorded fair value	0	0
Liability Derivatives, Gross fair value	32,938	16,912
Liability Derivatives, Netting arrangements	(2,547)	(6,088)
Liability Derivatives, Net recorded fair value	30,391	10,824
Short-Term Derivative Instruments [Member] | Commodity derivatives [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	2,547	6,088
Liability Derivatives, Gross fair value	31,310	15,007
Short-Term Derivative Instruments [Member] | Interest Rate Swaps [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	0	0
Liability Derivatives, Gross fair value	1,628	1,905
Long-Term Derivative Instruments [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	5,349	9,361
Asset Derivatives, Netting arrangements	(3,827)	(8,488)
Asset Derivatives, Net recorded fair value	1,522	873
Liability Derivatives, Gross fair value	9,182	9,335
Liability Derivatives, Netting arrangements	(3,827)	(8,488)
Liability Derivatives, Net recorded fair value	5,355	847
Long-Term Derivative Instruments [Member] | Commodity derivatives [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	5,349	9,361
Liability Derivatives, Gross fair value	8,584	8,488
Long-Term Derivative Instruments [Member] | Interest Rate Swaps [Member]
Derivative Instruments and Hedges, Assets [Abstract]
Total assets	0	0
Liability Derivatives, Gross fair value	$ 598	$ 847