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Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Detail) - Recurring - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Assets: |  |
Total assets | $ 107,018 | $ 495
Total liabilities | 104 | 135,567
Money market funds |  |
Assets: |  |
Total assets | 143 | 142
Commodity derivative instruments |  |
Assets: |  |
Total assets | 106,875 | 353
Total liabilities | 104 | 135,567
Level 1 |  |
Assets: |  |
Total assets | 143 | 142
Total liabilities | 0 | 0
Level 1 | Money market funds |  |
Assets: |  |
Total assets | 143 | 142
Level 1 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 0 | 0
Total liabilities | 0 | 0
Level 2 |  |
Assets: |  |
Total assets | 106,875 | 353
Total liabilities | 104 | 135,567
Level 2 | Money market funds |  |
Assets: |  |
Total assets | 0 | 0
Level 2 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 106,875 | 353
Total liabilities | 104 | 135,567
Level 3 |  |
Assets: |  |
Total assets | 0 | 0
Total liabilities | 0 | 0
Level 3 | Money market funds |  |
Assets: |  |
Total assets | 0 | 0
Level 3 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 0 | 0
Total liabilities | $ 0 | $ 0

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