Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
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Dec. 31, 2018 |
Dec. 31, 2017 |
Mar. 31, 2016 |
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
| Asset retirement obligation capitalized | $ 1,827 | $ 16,300 | |
| Asset retirement obligation, revised | 375 | $ (25,970) | |
| Level 3 | |||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
| Asset retirement obligation capitalized | 1,800 | ||
| Asset retirement obligation, revised | $ 400 | ||
| Level 3 | Investment in Grizzly Oil Sands ULC | |||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||
| Fair value of equity investment | $ 39,100 | ||
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- Definition Amount of asset retirement obligations incurred during the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Fair value portion of investments accounted under the equity method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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