Determination of Gain Recognized upon Disposition of PVG (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2010
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds, net of offering costs, units	8,827,429
Cash proceeds, net of offering costs, per unit	$ 15.76