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Long-term debt (Details)
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12 Months Ended | 1 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2012
USD ($)
project
|
Dec. 31, 2011
USD ($)
|
Dec. 31, 2012
Curtis Palmer
USD ($)
|
Dec. 31, 2011
Curtis Palmer
USD ($)
|
Dec. 31, 2012
Epsilon Power Partners
|
Dec. 31, 2012
Chambers Project [Member]
quarter
|
Dec. 31, 2012
Delta
quarter
|
Dec. 31, 2012
Gregory Project [Member]
|
Dec. 31, 2011
Purchase accounting fair value adjustments
USD ($)
|
Dec. 31, 2012
Minimum
|
Dec. 31, 2012
Maximum
|
Nov. 30, 2011
Senior unsecured notes, due 2018
USD ($)
|
Dec. 31, 2012
Senior unsecured notes, due 2018
USD ($)
|
Dec. 31, 2011
Senior unsecured notes, due 2018
USD ($)
|
Nov. 05, 2011
Senior unsecured notes, due 2018
USD ($)
|
Dec. 31, 2012
Senior unsecured notes, due June 2036
USD ($)
|
Dec. 31, 2012
Senior unsecured notes, due June 2036
CAD
|
Dec. 31, 2011
Senior unsecured notes, due June 2036
USD ($)
|
Dec. 31, 2012
Senior unsecured notes, due July 2014
USD ($)
|
Dec. 31, 2011
Senior unsecured notes, due July 2014
USD ($)
|
Dec. 31, 2012
Senior unsecured notes, due July 2014
Curtis Palmer
USD ($)
|
Dec. 31, 2012
Series A senior unsecured notes, due August 2015
USD ($)
|
Dec. 31, 2011
Series A senior unsecured notes, due August 2015
USD ($)
|
Dec. 31, 2012
Series B senior unsecured notes, due August 2017
USD ($)
|
Dec. 31, 2011
Series B senior unsecured notes, due August 2017
USD ($)
|
Dec. 31, 2012
Epsilon Power Partners term facility, due 2019
USD ($)
|
Dec. 31, 2011
Epsilon Power Partners term facility, due 2019
USD ($)
|
Dec. 31, 2012
Auburndale term loan, due 2013
|
Dec. 31, 2011
Auburndale term loan, due 2013
USD ($)
|
Dec. 31, 2012
Cadillac term loan, due 2025
USD ($)
|
Dec. 31, 2011
Cadillac term loan, due 2025
USD ($)
|
Dec. 31, 2012
Cadillac term loan, due 2025
Minimum
|
Dec. 31, 2012
Cadillac term loan, due 2025
Maximum
|
Dec. 31, 2012
Piedmont bridge loan, due 2013
USD ($)
|
Dec. 31, 2011
Piedmont bridge loan, due 2013
USD ($)
|
Dec. 31, 2012
Path 15 senior secured bonds
USD ($)
|
Dec. 31, 2011
Path 15 senior secured bonds
USD ($)
|
Dec. 31, 2012
Path 15 senior secured bonds
Purchase accounting fair value adjustments
USD ($)
|
Dec. 31, 2012
Path 15 senior secured bonds
Minimum
|
Dec. 31, 2012
Path 15 senior secured bonds
Maximum
|
Dec. 31, 2012
5.87% senior guaranteed notes, Series A, due August 15, 2017
|
Dec. 31, 2012
5.97% senior guaranteed notes, Series B, due August 15, 2019
|
Dec. 31, 2012
Senior credit facility
USD ($)
|
Dec. 31, 2012
Senior credit facility
Minimum
|
Dec. 31, 2012
Senior credit facility
Maximum
|
Dec. 31, 2012
Senior unsecured notes, due August 2019
USD ($)
|
Dec. 31, 2012
Meadow Creek construction loan, due 2013
USD ($)
|
Dec. 31, 2012
Meadow Creek construction loan, due 2013
Minimum
|
Dec. 31, 2012
Meadow Creek construction loan, due 2013
Maximum
|
Dec. 31, 2012
Construction term loan
USD ($)
|
Dec. 31, 2012
Cash grant loan
USD ($)
|
Dec. 31, 2012
Rockland term loan, due 2031
USD ($)
|
Dec. 31, 2012
Ridgeline working capital loan
USD ($)
|
Dec. 31, 2012
Ridgeline working capital loan
Minimum
|
Dec. 31, 2012
Ridgeline working capital loan
Maximum
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| Long-term debt | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total debt | $ 1,580,341,000 | $ 10,580,000 | $ 460,000,000 | $ 460,000,000 | $ 460,000,000 | $ 211,071,000 | 210,000,000 | $ 206,490,000 | $ 190,000,000 | $ 190,000,000 | $ 190,000,000 | $ 150,000,000 | $ 150,000,000 | $ 75,000,000 | $ 75,000,000 | $ 33,482,000 | $ 34,982,000 | $ 11,900,000 | $ 37,831,000 | $ 40,231,000 | $ 127,446,000 | $ 100,796,000 | $ 145,879,000 | $ 9,900,000 | $ 75,000,000 | $ 208,698,000 | $ 86,560,000 | $ 253,000 | |||||||||||||||||||||||||||
| Less current maturities | (121,203,000) | (20,958,000) | 3,000,000 | 1,500,000 | 7,000,000 | 2,400,000 | 3,791,000 | 55,061,000 | 9,400,000 | 8,667,000 | (59,508,000) | ||||||||||||||||||||||||||||||||||||||||||||
| Total long-term debt | 1,459,138,000 | 1,404,900,000 | 190,000,000 | 190,000,000 | 128,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Interest rate (as a percent) | 9.00% | 9.00% | 5.95% | 5.95% | 5.90% | 7.40% | 5.10% | 6.02% | 8.00% | 7.90% | 9.00% | 5.87% | 5.97% | 1.31% | 5.08% | 6.40% | 5.50% | 5.90% | |||||||||||||||||||||||||||||||||||||
| Percentage of ownership interest | 100.00% | 40.00% | 5.00% | 50.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Variable interest rate basis | Libor | U.S. Prime Rate, the London Interbank Offered Rate or the Canadian Prime Rate | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Amount drawn on the senior credit facility | 67,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Letters of credit issued but not drawn | 112,900,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Applicable margin (as a percent) | 3.50% | 2.75% | 0.75% | 3.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Bridge loan | 51,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of days of commercial operation after stimulus grant is expected to be received | 60 days | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Construction loan | 82,000,000 | 152,200,000 | 56,500,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||
| Percentage of par value at which debt was issued | 97.471% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Gross proceeds from senior notes | 448,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of projects not in compliance with covenants contained in project level debt | 1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of quarters used in calculating the debt service coverage ratio | 4 | 4 | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Period of historical project cash flows used to calculate debt service coverage ratio | 6 months | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Period of projected project cash flows used to calculate debt service coverage ratio | 6 months | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Maximum borrowing capacity before amendment | 100,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Maximum borrowing capacity | 300,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Maximum capacity to be utilized for letter of credit | 200,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Debt to EBITDA ratio, restriction on payment of dividend to shareholders | 7.25 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Principal payments on the maturities of debt due in next five years | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2013 | 121,203,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2014 | 207,845,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2015 | 170,473,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2016 | 19,138,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2017 | 94,954,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Thereafter | 966,728,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total debt | $ 1,580,341,000 | $ 10,580,000 | $ 460,000,000 | $ 460,000,000 | $ 460,000,000 | $ 211,071,000 | 210,000,000 | $ 206,490,000 | $ 190,000,000 | $ 190,000,000 | $ 190,000,000 | $ 150,000,000 | $ 150,000,000 | $ 75,000,000 | $ 75,000,000 | $ 33,482,000 | $ 34,982,000 | $ 11,900,000 | $ 37,831,000 | $ 40,231,000 | $ 127,446,000 | $ 100,796,000 | $ 145,879,000 | $ 9,900,000 | $ 75,000,000 | $ 208,698,000 | $ 86,560,000 | $ 253,000 | |||||||||||||||||||||||||||