Offering Costs and Formation Transaction Expenses - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012
Organization And Offering Costs [Line Items]
Accumulated correction impacted amount	$ 1,414,890		$ 790,019	$ 252,337
Incurred external offering cost	1,414,890
Offering costs	624,871	297,604
Offering costs due to Supervisor	208,303		127,671
Additional offering costs for work done by supervisor's employees	81,120	40,977
Adjustment
Organization And Offering Costs [Line Items]
Accumulated correction impacted amount			(213,500)
Incurred external offering cost				$ 38,837