Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivatives	$ 88,422,000	$ (68,131,000)	$ 37,427,000
Commodity derivative assets – current	78,793,000	4,131,000
Derivative assets, noncurrent	25,449,000	2,750,000
Derivative liabilities, noncurrent	28,434,000	3,385,000
Derivative Asset	104,242,000	6,881,000
Derivative liabilities, current	85,427,000	23,450,000
Derivative liabilities	113,861,000	26,835,000
Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative Asset	4,300,000
Commodity contracts | Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Commodity derivative assets – current	78,793,000	4,131,000
Derivative liabilities, current	81,772,000	23,450,000
Commodity contracts | Derivative assets/liabilities - noncurrent
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent	25,449,000	2,750,000
Derivative liabilities, noncurrent	26,789,000	3,385,000
Interest Rate Swap | Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Commodity derivative assets – current	0	0
Derivative liabilities, current	3,655,000	0
Interest Rate Swap | Derivative assets/liabilities - noncurrent
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent	0	0
Derivative liabilities, noncurrent	1,645,000	0
Fair Value, Measurements, Recurring | Commodity contracts
Derivatives, Fair Value [Line Items]
Commodity derivative assets – current	78,793,000	4,131,000
Derivative assets, noncurrent	25,449,000	2,750,000
Derivative liabilities, noncurrent	26,789,000	3,385,000
Derivative liabilities, current	(81,772,000)	$ (23,450,000)
Fair Value, Measurements, Recurring | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	1,645,000
Derivative liabilities, current	$ (3,655,000)