Offering Costs and Formation Transaction Expenses - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Registrant incurred capitalized external offering costs	$ 3,453,410
External offering costs	142,725	265,464
Offering costs due to Supervisor	93,376		451,082
Additional offering costs for work done by employees of Supervisor	83,271	49,099
Impact of error correction accumulated		$ 481,894