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Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Assets: |  |
Total assets | $ 4,792 | $ 107,018
Liabilities: |  |
Total liabilities | 28,934 | 104
Money market funds |  |
Assets: |  |
Total assets | 144 | 143
Commodity derivative instruments |  |
Assets: |  |
Total assets | 4,648 | 106,875
Liabilities: |  |
Total liabilities | 28,934 | 104
Level 1 |  |
Assets: |  |
Total assets | 144 | 143
Liabilities: |  |
Total liabilities | 0 | 0
Level 1 | Money market funds |  |
Assets: |  |
Total assets | 144 | 143
Level 1 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 0 | 0
Liabilities: |  |
Total liabilities | 0 | 0
Level 2 |  |
Assets: |  |
Total assets | 4,648 | 106,875
Liabilities: |  |
Total liabilities | 28,934 | 104
Level 2 | Money market funds |  |
Assets: |  |
Total assets | 0 | 0
Level 2 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 4,648 | 106,875
Liabilities: |  |
Total liabilities | 28,934 | 104
Level 3 |  |
Assets: |  |
Total assets | 0 | 0
Liabilities: |  |
Total liabilities | 0 | 0
Level 3 | Money market funds |  |
Assets: |  |
Total assets | 0 | 0
Level 3 | Commodity derivative instruments |  |
Assets: |  |
Total assets | 0 | 0
Liabilities: |  |
Total liabilities | $ 0 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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