Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) (USD $)	9 Months Ended
Sep. 30, 2012 MW
Square Butte PPA [Member]
Power Purchase Agreements [Line Items]
Generating Unit Capacity (MW)	455
Share of Plant Output (Percent)	50.00%
Total Debt Outstanding	$ 417,400,000
Annual Debt Service	44,000,000
Oliver Wind I PPA [Member]
Power Purchase Agreements [Line Items]
Share of Plant Output (MW)	50
Term of PPA (Years)	25
Fixed Capacity Carges	0
Oliver Wind II PPA [Member]
Power Purchase Agreements [Line Items]
Share of Plant Output (MW)	48
Term of PPA (Years)	25
Fixed Capacity Carges	$ 0
Manitoba Hydro PPA (expires April 2015) [Member]
Power Purchase Agreements [Line Items]
Share of Plant Output (MW)	50
Manitoba Hydro PPA (expires April 2022) [Member]
Power Purchase Agreements [Line Items]
Share of Plant Output (MWh)	1,000,000
Manitoba Hydro PPA (expires 2035) [Member]
Power Purchase Agreements [Line Items]
Share of Plant Output (MW)	250
Term of PPA (Years)	15
Transmission Line Capacity (kV)	500

Long-Term Contract for Purchase of Electric Power, Fixed Capacity Carges

No definition available.

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- Definition

The generating capacity of a production plant constructed and financed by a public utility district, cooperative, or other organization with whom exists a long-term contract to purchase electric power.

+ References

No definition available.

+ Details

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- Definition

Share of plant output being purchased in megawatts under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

+ References

No definition available.

+ Details

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- Definition

Share of plant output being purchased in megawatthours under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

+ References

No definition available.

+ Details

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- Definition

Term in years of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

+ References

No definition available.

+ Details

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- Definition

Capacity of a transmission line in kilovolts.

+ References

No definition available.

+ Details

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- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.D)

-URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section D

+ Details

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- Definition

Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service. If the utility is obligated to pay certain minimum amounts which cover debt service requirements whether or not the plant is operating, the amount can be disclosed here.

+ References

+ Details

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- Details

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- Definition

Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

+ References

+ Details

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