Represents the amount of contribution made to cover shortfall resulting from the federal sequester on spending.

No definition available.

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- Definition

Represents the amount of contribution made to cover shortfall resulting from lower grant-eligible costs.

+ References

No definition available.

+ Details

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- Definition

Represents the estimated shortfall in the recovery of capital cost.

+ References

No definition available.

+ Details

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- Definition

Represents the number of covenant failures resulting in the non-recourse debt being callable as on the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Represents the number of days of commercial operation after stimulus grant is expected to be received from the U.S. Treasury.

+ References

No definition available.

+ Details

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- Definition

Represents the recovery as a percentage of capital cost under 1603 federal grant program.

+ References

No definition available.

+ Details

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- Definition

Short-Term financing which is expected to be paid back relatively quickly, such as by a subsequent longer-term loan. Also called swing loan or bridge financing.

+ References

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- Definition

This element represents the carrying value of a short-term real estate loan to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project, usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 52

-IssueDate 2006-05-01

-Chapter 8

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20

-Article 5

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- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Decrease for amounts repaid on the debt instrument for the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph f

-Article 4

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Details

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for a specific purpose other than for financing goods acquired for inventory or imminent delivery to a customer.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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-Subparagraph (SX 210.5-02.22)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Long-term debt (Details) In Millions, unless otherwise specified																						3 Months Ended											1 Months Ended	3 Months Ended
	Apr. 30, 2013 USD ($)	Mar. 31, 2013 USD ($) item	Dec. 31, 2012 USD ($)	Mar. 31, 2013 Senior unsecured notes, due 2018 USD ($)	Dec. 31, 2012 Senior unsecured notes, due 2018 USD ($)	Mar. 31, 2013 Senior unsecured notes, due June 2036 USD ($)	Mar. 31, 2013 Senior unsecured notes, due June 2036 CAD	Dec. 31, 2012 Senior unsecured notes, due June 2036 USD ($)	Dec. 31, 2012 Senior unsecured notes, due June 2036 CAD	Mar. 31, 2013 Senior unsecured notes, due July 2014 USD ($)	Dec. 31, 2012 Senior unsecured notes, due July 2014 USD ($)	Mar. 31, 2013 Series A senior unsecured notes, due August 2015 USD ($)	Dec. 31, 2012 Series A senior unsecured notes, due August 2015 USD ($)	Mar. 31, 2013 Series B senior unsecured notes, due August 2017 USD ($)	Dec. 31, 2012 Series B senior unsecured notes, due August 2017 USD ($)	Mar. 31, 2013 Epsilon Power Partners term facility, due 2019 USD ($)	Dec. 31, 2012 Epsilon Power Partners term facility, due 2019 USD ($)	Mar. 31, 2013 Cadillac term loan, due 2025 USD ($)	Dec. 31, 2012 Cadillac term loan, due 2025 USD ($)	Mar. 31, 2013 Cadillac term loan, due 2025 Minimum	Mar. 31, 2013 Cadillac term loan, due 2025 Maximum	Mar. 31, 2013 Piedmont bridge loan, due 2013 USD ($)	Jun. 30, 2013 Piedmont bridge loan, due 2013 USD ($)	Dec. 31, 2012 Piedmont bridge loan, due 2013 USD ($)	Mar. 31, 2013 Senior credit facility USD ($)	Mar. 31, 2013 Senior credit facility Minimum	Mar. 31, 2013 Senior credit facility Maximum	Mar. 31, 2013 Meadow Creek term loan, due 2030 USD ($)	Dec. 31, 2012 Meadow Creek term loan, due 2030 USD ($)	Mar. 31, 2013 Meadow Creek term loan, due 2030 Minimum	Mar. 31, 2013 Meadow Creek term loan, due 2030 Maximum	Mar. 31, 2013 Construction term loan USD ($)	Apr. 30, 2013 Cash grant loan USD ($)	Mar. 31, 2013 Cash grant loan USD ($)	Mar. 31, 2013 Rockland term loan, due 2031 USD ($)	Dec. 31, 2012 Rockland term loan, due 2031 USD ($)	Mar. 31, 2013 Other long-term debt USD ($)	Dec. 31, 2012 Other long-term debt USD ($)	Mar. 31, 2013 Other long-term debt Minimum	Mar. 31, 2013 Other long-term debt Maximum
Long-term debt
Total debt				$ 460.0	$ 460.0	$ 206.7	210.0	$ 211.1	210.0	$ 190.0	$ 190.0	$ 150.0	$ 150.0	$ 75.0	$ 75.0	$ 32.7	$ 33.5	$ 37.2	$ 37.8			$ 127.6		$ 127.4				$ 229.3	$ 208.7						$ 86.5	$ 86.5	$ 0.8	$ 0.3
Less current maturities		121.7	121.2													3.5	3.0	2.3	2.4			55.1		55.1				59.5	59.5						1.2	1.2	0.1
Total long-term debt		1,474.1	1,459.1
Interest rate (as a percent)				9.00%		6.00%	6.00%			5.90%		5.90%		6.00%		7.40%				6.00%	8.00%									1.30%	5.10%				6.40%				5.50%	6.70%
Variable interest rate basis																						Libor
Amount drawn on the senior credit facility																									64.1
Letters of credit issued but not drawn	82.5																								111.6
Applicable margin (as a percent)																						3.50%			2.80%	0.80%	3.00%
Bridge loan																							51.0
Expected shortfall in recovery of capital cost																						2.0
Recovery as a percentage of capital cost																						30.00%
Number of days of commercial operation after stimulus grant is expected to be received																						60 days
Construction loan																						82.0										172.8		56.5
Repayment of debt from proceeds from 1603 grant with U.S. Treasury																																	49.0
Contribution to cover shortfall resulting from lower grant-eligible costs																																		2.8
Number of covenant failures resulting in the non-recourse debt being callable		0
Maximum borrowing capacity																									300.0
Maximum capacity to be utilized for letter of credit																									200.0
Contribution to cover shortfall resulting from the federal sequester on spending																																		$ 4.7