Equity method investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Operating results
Revenue	$ 53,328	$ 46,415
Project expenses	45,492	42,543
Project other income (expense)	(4,889)	(2,561)
Project income (loss)	2,947	1,311
Chambers
Operating results
Revenue	13,227	13,269
Project expenses	9,753	9,380
Project other income (expense)	(1,193)	(427)
Project income (loss)	2,281	3,462
Badger Creek
Operating results
Revenue	1,179	3,316
Project expenses	1,137	2,983
Project other income (expense)	(4)
Project income (loss)	38	333
Gregory
Operating results
Revenue	4,315	7,181
Project expenses	5,780	6,630
Project other income (expense)	(83)	(38)
Project income (loss)	(1,548)	513
Orlando
Operating results
Revenue	10,812	9,926
Project expenses	10,093	9,463
Project other income (expense)	(14)	(30)
Project income (loss)	705	433
Selkirk
Operating results
Revenue	12,062	10,902
Project expenses	10,335	12,659
Project other income (expense)	(65)	(1,636)
Project income (loss)	1,662	(3,393)
Other
Operating results
Revenue	11,733	1,821
Project expenses	8,394	1,428
Project other income (expense)	(3,530)	(430)
Project income (loss)	$ (191)	$ (37)