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Derivative and Hedging Instruments (Details-5) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 USD ($) counterparty | Jun. 30, 2015 USD ($) | Jun. 30, 2016 USD ($) counterparty | Jun. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Counterparties in net liability position or default [Abstract] |  |  |  |  |
Derivative, net liability position of counterparties (less than $0.1 million) | $ 0 |  | $ 0 |  | $ 100
Number of counterparties in default | counterparty | 0 |  | 0 |  |
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | $ 417 | $ 578 | $ 1,424 | $ 998 |
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | 0 | (2) | 1,814 | 1,759 |
Financial Transmission Rights [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | 136 | (255) | 68 | (374) |
Financial Transmission Rights [Member] | Cost Of Gas Sold Expense [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | 0 | 0 | 0 | 0 |
Purchased Power Agreement [Member] |  |  |  |  |
Derivative collateral required to be posted for PPA [Abstract] |  |  |  |  |
Minimum collateral that may be required to be posted | 20,000 |  | 20,000 |  |
Maximum collateral that may be required to be posted | 40,000 |  | 40,000 |  |
Collateral posted | 0 |  | 0 |  |
Purchased Power Agreement [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | 1,226 | 570 | 2,595 | 1,591 |
Purchased Power Agreement [Member] | Cost Of Gas Sold Expense [Member] |  |  |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |  |  |
Realized losses (gains) on income statement | $ 0 | $ 0 | $ 0 | $ 0 |

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