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Equity Investments (Narrative) (Details) $ / shares in Units, a in Thousands, shares in Millions |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 05, 2017 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) | Mar. 31, 2018 USD ($) a project | Mar. 31, 2017 USD ($) | Dec. 31, 2014 entity | Sep. 30, 2014 a | Dec. 31, 2014 USD ($) | Feb. 17, 2017 $ / shares | Dec. 15, 2016 $ / shares | Apr. 30, 2015 bbl | Mar. 31, 2015 | Jun. 30, 2014 bbl
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ 13,536,000 | $ (4,907,000) |  |  |  |  |  |  |  |
Distributions from equity method investments |  |  | 750,000 | 631,000 |  |  |  |  |  |  |  |
Payments for equity method investments |  |  | 1,569,000 | 10,673,000 |  |  |  |  |  |  |  |
Share price (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 19.48 | $ 20.96 |  |  |
Tatex Thailand III LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Distributions from equity method investments |  | $ 200,000 |  |  |  |  |  |  |  |  |  |
Tatex Thailand II, LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ 41,000 | 243,000 |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  | 23.50% |  |  |  |  |  |  |  |  |
Grizzly Oil Sands ULC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Gas and oil area, reserve (acres) | a |  |  | 830 |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ (330,000) | (365,000) |  |  |  |  |  |  |  |
Number of oil sand projects | project |  |  | 3 |  |  |  |  |  |  |  |  |
Production volume (in Bbls/day) | bbl |  |  |  |  |  |  |  |  |  | 2,200 |  | 11,300
Other than temporary impairment loss |  |  | $ 0 | 0 |  |  |  |  |  |  |  |
Equity method investment, amount of cash calls, based on proportionate ownership interest |  |  | 1,600,000 |  |  |  |  |  |  |  |  |
Equity method investments, increase (decrease) due to foreign currency translation adjustment |  |  | $ (5,300,000) | 1,300,000 |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  | 24.9999% |  |  |  |  |  |  |  |  |
Windsor Midstream LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ 0 | 311,000 |  |  |  |  |  |  |  |
Distributions from equity method investments |  |  | $ 0 | 200,000 |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  | 22.50% |  |  |  |  |  |  |  |  |
Coronado Midstream LLC | Windsor Midstream LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  |  |  |  |  |  |  |  |  | 28.40% |
Sturgeon Acquisitions LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ 0 | (68,000) |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  | 0.00% |  | 25.00% |  | 25.00% |  |  |  |  |
Payments for equity method investments |  |  |  |  |  |  | $ 20,700,000 |  |  |  |  |
Gain on sale of equity method investments | $ 12,500,000 |  |  |  |  |  |  |  |  |  |  |
Mammoth Energy Services LP |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Equity method investments, increase (decrease) due to foreign currency translation adjustment |  |  | $ (200,000) | 100,000 |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  |  | 25.10% |  | 30.50% |  | 30.50% |  |  |  |  |
Number of entities contributed for ownership interest | entity |  |  |  |  | 4 |  |  |  |  |  |  |
Shares received from equity method investee in exchange for ownership interest (in shares) | shares | 2.0 |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) | $ / shares | $ 18.50 |  |  |  |  |  |  |  |  |  |  |
Strike Force Midstream LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments and investments in subsidiaries |  |  | $ 357,000 | (2,541,000) |  |  |  |  |  |  |  |
Distributions from equity method investments |  |  | $ 800,000 | 400,000 |  |  |  |  |  |  |  |
Equity method investment, ownership interest, percent |  | 25.00% | 25.00% |  |  |  |  |  |  |  |  |
Payments for equity method investments |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |
Phu Horm Field | Apico Llc |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Gas and oil area, reserve (acres) | a |  |  | 180 |  |  |  |  |  |  |  |  |
Concession Acreage in Southeast Asia | Tatex Thailand III LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Gas and oil area, reserve (acres) | a |  |  |  |  |  | 245 |  |  |  |  |  |
Apico Llc | Tatex Thailand II, LLC |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  | 8.50% |  |  |  |  |  |  |  |  |
Strike Force Midstream LLC | Rice Energy Inc |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent |  | 75.00% |  |  |  |  |  |  |  |  |  |

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