Long-term debt (Details)																												3 Months Ended		3 Months Ended
	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Mar. 31, 2012 Curtis Palmer USD ($)	Mar. 31, 2012 Guarantor Subsidiaries USD ($)	Mar. 31, 2012 Senior Notes, due 2018 USD ($)	Dec. 31, 2011 Senior Notes, due 2018 USD ($)	Mar. 31, 2012 Senior unsecured notes, due June 2036 USD ($)	Mar. 31, 2012 Senior unsecured notes, due June 2036 CAD	Dec. 31, 2011 Senior unsecured notes, due June 2036 USD ($)	Mar. 31, 2012 Senior unsecured notes, due July 2014 USD ($)	Dec. 31, 2011 Senior unsecured notes, due July 2014 USD ($)	Mar. 31, 2012 Senior unsecured notes, due August 2017 USD ($)	Dec. 31, 2011 Senior unsecured notes, due August 2017 USD ($)	Mar. 31, 2012 Senior unsecured notes, due August 2019 USD ($)	Dec. 31, 2011 Senior unsecured notes, due August 2019 USD ($)	Mar. 31, 2012 Epsilon Power Partners term facility, due 2019 USD ($)	Dec. 31, 2011 Epsilon Power Partners term facility, due 2019 USD ($)	Mar. 31, 2012 Path 15 senior secured bonds USD ($)	Dec. 31, 2011 Path 15 senior secured bonds USD ($)	Mar. 31, 2012 Path 15 senior secured bonds Minimum	Mar. 31, 2012 Path 15 senior secured bonds Maximum	Mar. 31, 2012 Auburndale term loan, due 2013 USD ($)	Dec. 31, 2011 Auburndale term loan, due 2013 USD ($)	Mar. 31, 2012 Cadillac term loan, due 2025 USD ($)	Dec. 31, 2011 Cadillac term loan, due 2025 USD ($)	Mar. 31, 2012 Cadillac term loan, due 2025 Minimum	Mar. 31, 2012 Cadillac term loan, due 2025 Maximum	Mar. 31, 2012 Piedmont bridge loan, due 2013 USD ($)	Dec. 31, 2011 Piedmont bridge loan, due 2013 USD ($)	Mar. 31, 2012 Canadian Hills construction loan, due 2013 USD ($)	Mar. 31, 2012 Senior credit facility USD ($)
Long-term debt
Total debt		$ 1,415,278,000			$ 460,000,000	$ 460,000,000	$ 210,526,000	210,000,000	$ 206,490,000	$ 190,000,000	$ 190,000,000	$ 150,000,000	$ 150,000,000	$ 75,000,000	$ 75,000,000	$ 34,608,000	$ 34,982,000	$ 145,880,000	$ 145,879,000			$ 10,150,000	$ 11,900,000	$ 39,631,000	$ 40,231,000			$ 108,863,000	$ 100,796,000
Purchase accounting fair value adjustments	10,398,000	10,580,000
Less current maturities	(246,520,000)	(20,958,000)		(246,520,000)
Total long-term debt	1,364,685,000	1,404,900,000	190,000,000	714,685,000																										176,149,000
Interest rate (as a percent)					9.00%		5.95%	5.95%		5.90%		5.87%		5.97%		7.40%				7.90%	9.00%	5.10%				6.02%	8.00%
Variable interest rate basis																												Libor		Libor
Amount drawn on the senior credit facility																															72,800,000
Letters of credit issued but not drawn																															$ 139,100,000
Applicable margin (as a percent)																												3.50%		3.00%	2.75%