Distributions - Distributions Declared Per Common Share (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule Of Group Distributions [Line Items]
Distributions declared per common share	$ 0.15	$ 0.15	$ 0.45	$ 0.45
Less: Distributions declared in the current period, and paid in the subsequent period			$ (0.15)	$ (0.15)
Add: Distributions declared in the prior year, and paid in the current year			$ 0.15	$ 0.15
Distributions paid per common share			$ 0.45	$ 0.45