In Kind Distributions Paid to Class B Unitholders (Detail)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Distribution Made to Member or Limited Partner [Line Items]
Units	511,000	[1]
Period 1
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Feb. 21, 2011		Feb. 16, 2010	Feb. 12, 2009
Payment Date	Feb. 28, 2011		Feb. 26, 2010	Feb. 27, 2009
Period 2
Distribution Made to Member or Limited Partner [Line Items]
Record Date	May 16, 2011		May 17, 2010	May 11, 2009
Payment Date	May 31, 2011		May 28, 2010	May 29, 2009
Period 3
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Aug. 15, 2011		Aug. 16, 2010	Aug. 07, 2009
Payment Date	Aug. 31, 2011		Aug. 31, 2010	Aug. 31, 2009
Period 4
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Nov. 14, 2011		Nov. 15, 2010	Nov. 12, 2009
Payment Date	Nov. 30, 2011		Nov. 30, 2010	Nov. 30, 2009
Class B Units
Distribution Made to Member or Limited Partner [Line Items]
Units	511,399
Class B Units | Period 1
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Feb. 21, 2011
Payment Date	Feb. 28, 2011
Units	122,244
Class B Units | Period 2
Distribution Made to Member or Limited Partner [Line Items]
Record Date	May 16, 2011
Payment Date	May 31, 2011
Units	127,046
Class B Units | Period 3
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Aug. 15, 2011
Payment Date	Aug. 31, 2011
Units	133,068
Class B Units | Period 4
Distribution Made to Member or Limited Partner [Line Items]
Record Date	Nov. 14, 2011
Payment Date	Nov. 30, 2011
Units	129,041

[1] Amounts presented through the date of the Merger represent historical BGH units outstanding.