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Fair Value Measurements - Schedule of Reconciliation of Changes in Assets and Liabilities Measured at Fair Value On a Recurring Basis (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Net unrealized gains on oil price risk derivatives | $ 160 |
Recurring Measurements [Member] |  |
Fair value | 1,976 | $ 1,302
Acquisition of investment | 777 | 750
Issuance of warrants |  | 1,240
Other comprehensive loss | (8) | 3
Net unrealized gains on oil price risk derivatives | (26) |
Net unrealized gain on warrant valuation | 170 | (210)
Net unrealized loss on Anfield Shares | (839) | (58)
Offset of derivative assets and liabilities |  | (194)
Cash settlements paid | (135) | (857)
Fair value | 1,915 | 1,976
Level 2 [Member] | Recurring Measurements [Member] | Crude Oil Derivative , Assets [Member] |  |
Fair value |  | 1,634
Acquisition of investment |  |
Issuance of warrants |  |
Other comprehensive loss |  |
Net unrealized gains on oil price risk derivatives |  |
Net unrealized gain on warrant valuation |  |
Net unrealized loss on Anfield Shares |  |
Offset of derivative assets and liabilities |  | (194)
Cash settlements paid |  | (1,440)
Fair value |  |
Level 2 [Member] | Recurring Measurements [Member] | Crude Oil Derivative , Liabilities [Member] |  |
Fair value |  |
Acquisition of investment |  |
Issuance of warrants |  |
Other comprehensive loss |  |
Net unrealized gains on oil price risk derivatives | (26) |
Net unrealized gain on warrant valuation |  |
Net unrealized loss on Anfield Shares |  |
Offset of derivative assets and liabilities |  |
Cash settlements paid | (135) |
Fair value | (161) |
Level 2 [Member] | Recurring Measurements [Member] | Sutter Gold Mining Company [Member] | Equity Securities [Member] |  |
Fair value | 16 | 13
Acquisition of investment |  |
Issuance of warrants |  |
Other comprehensive loss | (8) | 3
Net unrealized gains on oil price risk derivatives |  |
Net unrealized gain on warrant valuation |  |
Net unrealized loss on Anfield Shares |  |
Offset of derivative assets and liabilities |  |
Cash settlements paid |  |
Fair value | 8 | 16
Level 1 [Member] | Recurring Measurements [Member] | Anfield [Member] | Equity Securities [Member] |  |
Fair value | 930 | 238
Acquisition of investment | 777 | 750
Issuance of warrants |  |
Other comprehensive loss |  |
Net unrealized gains on oil price risk derivatives |  |
Net unrealized gain on warrant valuation |  |
Net unrealized loss on Anfield Shares | (839) | (58)
Offset of derivative assets and liabilities |  |
Cash settlements paid |  |
Fair value | 868 | 930
Level 3 [Member] | Recurring Measurements [Member] | Executive Retirement Programme Liabilities [Member] |  |
Fair value |  | (583)
Acquisition of investment |  |
Issuance of warrants |  |
Other comprehensive loss |  |
Net unrealized gains on oil price risk derivatives |  |
Net unrealized gain on warrant valuation |  |
Net unrealized loss on Anfield Shares |  |
Offset of derivative assets and liabilities |  |
Cash settlements paid |  | 583
Fair value |  |
Level 3 [Member] | Recurring Measurements [Member] | Warrant Liability [Member] |  |
Fair value | 1,030 |
Acquisition of investment |  |
Issuance of warrants |  | 1,240
Other comprehensive loss |  |
Net unrealized gains on oil price risk derivatives |  |
Net unrealized gain on warrant valuation | 170 | (210)
Net unrealized loss on Anfield Shares |  |
Offset of derivative assets and liabilities |  |
Cash settlements paid |  |
Fair value | $ 1,200 | $ 1,030

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