Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions) (Detail) bbl in Thousands, MMBTU in Thousands, $ in Thousands	Dec. 31, 2020 USD ($) bbl MMBTU	Dec. 31, 2019 USD ($) bbl MMBTU
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	3,056	1,214
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 8,341	$ 2,796
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	6,391	2,148
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (32,112)	$ (6,916)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	9,281	8,295
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 1,529	$ 2,131
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	15,079	2,689
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (3,265)	$ (70)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	6,391	2,172
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 32,670	$ 7,208
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	3,056	1,190
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (8,264)	$ (2,652)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	17,636	2,689
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 3,451	$ 83
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	6,724	8,295
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (1,458)	$ (2,039)