Risk Management and Derivative Financial Instruments (Details 3) $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($) item MWh $ / item
Transmission congestion rights (TCR) - 2015
Procurement guidelines
Monthly MWH Hedged \| MWh	1,430.0
Monthly MWH Hedged, estimated fair value \| $	$ 590
Electric \| Natural Gas Usage - Remainder 2016
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	56.00%
Dth Hedged Physical	2,676,000
Dth Hedged Financial	3,860,000
Average Price (in dollars per dth) \| $ / item	3.540
Electric \| Natural Gas Usage - 2017
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	41.00%
Dth Hedged Physical	782,900
Dth Hedged Financial	5,210,000
Average Price (in dollars per dth) \| $ / item	3.350
Electric \| Natural Gas Usage - 2018
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	20.00%
Dth Hedged Physical	565,000
Dth Hedged Financial	2,460,000
Average Price (in dollars per dth) \| $ / item	3.330
Electric \| Natural Gas Forward 2019
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	10.00%
Dth Hedged Financial	1,460,000
Average Price (in dollars per dth) \| $ / item	2.960
Electric \| Current Year Procurement Guidelines
Procurement guidelines
Maximum percentage of volume to be hedged in any given month	100.00%
Maximum flexibility to hedge any future year's expected requirements (as a percent)	80.00%
Electric \| First Year Procurement Guidelines
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	60.00%
Electric \| Second Year Procurement Guidelines
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	40.00%
Electric \| Third Year Procurement Guidelines
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	20.00%
Electric \| Fourth Year Procurement Guidelines
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	10.00%
Electric \| High end of range \| Current Year Procurement Guidelines
Volumes and percentage of anticipated volume of natural gas usage
% Hedged	100.00%

No definition available.

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- Definition

Represents the maximum flexibility to hedge any future year's expected requirements.

+ References

No definition available.

+ Details

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Maximum percentage of volume to be hedged in any given month.

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No definition available.

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- Definition

Represents the aggregate notional amount of derivative expressed in nonmonetary units.

+ References

No definition available.

+ Details

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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- Definition

The notional amount of financial derivatives expressed in nonmonetary units.

+ References

No definition available.

+ Details

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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

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- Definition

The average forward price on the group of price risk forward or futures contracts, such as gas futures contracts.

+ References

No definition available.

+ Details

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- Definition

The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

+ References

No definition available.

+ Details

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