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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
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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)

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