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Derivative and Hedging Instruments (Details-1) $ in Thousands | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2016 USD ($) Dth MWh MW | Dec. 31, 2015 USD ($) Dth MWh MW | Mar. 31, 2016 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Other Current Assets [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Derivative fair value, net | $ 659 | $ 1,208 | $ 655 | $ 455 | $ 268 | $ 1,001
Commodity Contracts And Financial Transimission Rights [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Derivative fair value, net | $ 1,700 | $ (800) |  |  |  |
Commodity Derivative Contracts [Member] |  |  |  |  |  |
Gross Notional Volume of Open Derivatives |  |  |  |  |  |
Notional amount, energy measure (in MWh) | MWh | 479,725 | 355,580 |  |  |  |
Notional amount, decatherm measure (in Dth) | Dth | 1,887,500 | 5,037,500 |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Asset Derivatives, fair value, gross basis | $ 1,957 | $ 290 |  |  |  |
Liability Derivatives, fair value, gross basis | 272 | 1,336 |  |  |  |
Commodity Derivative Contracts [Member] | Other Current Assets [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Asset Derivatives, fair value, gross basis | 1,814 | 146 |  |  |  |
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Asset Derivatives, fair value, gross basis | 143 | 144 |  |  |  |
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Liability Derivatives, fair value, gross basis | 212 | 1,266 |  |  |  |
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Liability Derivatives, fair value, gross basis | $ 60 | $ 70 |  |  |  |
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |
Derivatives Fair Value [Line Items] |  |  |  |  |  |
Maximum term of derivative hedging contract | 4 years |  |  |  |  |
Financial Transmission Rights [Member] |  |  |  |  |  |
Gross Notional Volume of Open Derivatives |  |  |  |  |  |
Notional amount, power measure (in MW) | MW | 5,653 | 2,000 |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Asset Derivatives, fair value, gross basis | $ 34 | $ 234 |  |  |  |
Financial Transmission Rights [Member] | Other Current Assets [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Asset Derivatives, fair value, gross basis | 34 | 234 |  |  |  |
Financial Transmission Rights [Member] | Derivative Liability (Current) [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Liability Derivatives, fair value, gross basis | 0 | 0 |  |  |  |
PPA [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Derivative fair value, net | (52,200) | (53,300) |  |  |  |
Liability Derivatives, fair value, gross basis | 52,240 | 53,270 |  |  |  |
PPA [Member] | Derivative Liability (Current) [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Liability Derivatives, fair value, gross basis | 8,650 | 8,340 |  |  |  |
PPA [Member] | Derivative Liability (Long-term) [Member] |  |  |  |  |  |
Derivative fair values [Abstract] |  |  |  |  |  |
Liability Derivatives, fair value, gross basis | $ 43,590 | $ 44,930 |  |  |  |

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