Offering Costs and Formation Transaction Expenses - Additional Information (Detail) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Registrant incurred capitalized external offering costs	$ 3,669,736
External offering costs	359,051	830,055
Offering costs due to Supervisor	296,499		451,082
Additional offering costs for work done by employees of Supervisor	91,729	80,188
Impact of error correction accumulated		$ 538,123