Fair Value Measurements - Fair Value Level 3 Inputs, Quantitative Information (Details)
$ in Thousands |
9 Months Ended |
12 Months Ended |
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Sep. 30, 2016
USD ($)
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Dec. 31, 2015
USD ($)
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Mar. 31, 2016
USD ($)
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Sep. 30, 2015
USD ($)
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Mar. 31, 2015
USD ($)
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Dec. 31, 2014
USD ($)
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| Energy derivative [Member] | Fair Value, Measurements, Recurring [Member] |
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
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| Fair value |
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$ 63,683
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| Energy derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member] |
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
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| Fair Value Inputs, Price Per MWh |
14.90
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12.48
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| Fair Value Inputs, Discount Rate |
0.85%
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0.61%
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| Energy derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member] |
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
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| Fair Value Inputs, Price Per MWh |
69.20
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74.94
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| Fair Value Inputs, Discount Rate |
1.04%
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1.46%
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| Energy derivative [Member] | Fair Value, Measurements, Recurring [Member] |
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
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| Fair value |
$ 48,713
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$ 63,683
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$ 49,531
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$ 66,075
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$ 61,445
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$ 64,475
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