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Fair Value Measurements (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets | $ 142,794,000 | $ 78,391,000 |
Asset retirement obligation capitalized | 8,800,000 | 9,295,000 | $ 3,556,000
Equity investments | 242,393,000 | 369,581,000 |
Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities | 0 |  |
Level 1 | Derivative Instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets | 0 | 0 |
Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities | 7,372,000 |  |
Level 2 | Derivative Instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets | 193,882,000 | 102,839,000 |
Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities | 0 |  |
Asset retirement obligation capitalized | 8,800,000 |  |
Level 3 | Derivative Instruments |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets | 0 | 0 |
Investment in Grizzly Oil Sands ULC |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Equity investments | $ 50,645,000 | $ 180,218,000 |

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