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, 2019 USD ($) MMBTU bbl	Dec. 31, 2018 USD ($) MMBTU bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	1,214	2,416
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 2,796	$ 24,332
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	2,148	415
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (6,916)	$ (646)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	8,295	5,745
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 2,131	$ 417
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	2,689	9,314
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (70)	$ (1,272)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	2,172	415
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 7,208	$ 646
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	1,190	2,416
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (2,652)	$ (24,009)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	2,689	10,236
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 83	$ 1,373
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	8,295	4,823
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (2,039)	$ (393)