Investment In BBEP (Financial Statement) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 BBEP [Member]	Dec. 31, 2010 BBEP [Member]
Current assets	$ 217,664	$ 238,172	$ 120,781	$ 130,017
Property, plant and equipment - net	3,376,805	3,067,845	1,712,096	1,722,295
Other assets			46,255	77,855
Current liabilities	415,638	463,100	103,103	101,317
Long-term debt	10,000		427,364	528,116
Other non-current liabilities	28,461	28,461	116,600	91,477
Total equity	$ 1,117,794	$ 1,059,408	$ 1,232,065	$ 1,209,257