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Derivative Instruments Schedule of Futures (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015
Derivative [Line Items] |  |
Derivative, Fair Value, Net | $ (16,649) | $ (2,542)
Futures [Member] | Short [Member] |  |
Derivative [Line Items] |  |
Derivative notional | (18,000) | (21,000)
Derivative, Fair Value, Net | $ (4) | $ 18
Derivative, Average Remaining Maturity | 10 months 6 days | 11 months 21 days
Futures [Member] | Short [Member] | Year 2016 [Member] |  |
Derivative [Line Items] |  |
Derivative notional | $ (9,000) | $ (12,000)
Derivative, Fair Value, Net | $ 1 | $ 10
Derivative, Average Remaining Maturity | 5 months 20 days | 7 months 4 days
Futures [Member] | Short [Member] | Year 2017 [Member] |  |
Derivative [Line Items] |  |
Derivative notional | $ (9,000) | $ (9,000)
Derivative, Fair Value, Net | $ (5) | $ 8
Derivative, Average Remaining Maturity | 14 months 23 days | 17 months 24 days

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611 + Details
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