Investment In BBEP (Operations Statement) (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Jun. 30, 2011 BBEP [Member]		Jun. 30, 2010 BBEP [Member]		Jun. 30, 2011 BBEP [Member]		Jun. 30, 2010 BBEP [Member]		Jun. 30, 2011 Commodity Derivative [Member]	Jun. 30, 2010 Commodity Derivative [Member]	Jun. 30, 2011 Commodity Derivative [Member]	Jun. 30, 2010 Commodity Derivative [Member]	Jun. 30, 2011 Interest Rate Swaps [Member]	Jun. 30, 2010 Interest Rate Swaps [Member]	Jun. 30, 2011 Interest Rate Swaps [Member]	Jun. 30, 2010 Interest Rate Swaps [Member]
Revenue					$ 142,368,000	[1]	$ 134,216,000	[1]	$ 147,829,000	[1]	$ 305,645,000	[1]
Operating expenses	191,912,000	172,608,000	574,662,000	438,624,000	72,929,000		73,621,000		226,349,000		216,170,000
Operating income (loss)	67,981,000	65,092,000	145,864,000	249,804,000	69,439,000		60,595,000		(78,520,000)		89,475,000
Interest and other					11,300,000	[2]	6,437,000	[2]	30,363,000	[2]	18,130,000	[2]
Income tax expense (benefit)	16,414,000	18,268,000	39,946,000	71,569,000	616,000		561,000		(825,000)		(469,000)
Noncontrolling interests					68,000		28,000		137,000		118,000
Net income (loss) available to BBEP	28,686,000	21,803,000	66,515,000	116,794,000	57,455,000		53,569,000		(108,195,000)		71,696,000
Unrealized gains (losses)													$ 48,200,000	$ 33,200,000	$ (146,700,000)	$ 18,400,000	$ (2,100,000)	$ 1,500,000	$ 2,400,000	$ 3,900,000

[1] For the three months ended June 30, 2011 and 2010, unrealized gains of $48.2 million and $33.2 million on commodity derivatives were recognized, respectively. For the nine months ended June 30, 2011 and 2010, unrealized losses of $146.7 million and unrealized gains of $18.4 million on commodity derivatives were recognized, respectively.

[2] The three months ended June 30, 2011 and 2010 included unrealized losses of $2.1 million and unrealized gains of $1.5 million, respectively, from interest rate swaps. The nine months ended June 30, 2011 and 2010 included unrealized gains of $2.4 million and $3.9 million, respectively, from interest rate swaps.