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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, 2019 USD ($) MMBTU bbl | Dec. 31, 2018 USD ($) MMBTU bbl
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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)

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