Subsequent Events - Narrative (Detail) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2013 Subsequent Event [Member]	Jun. 30, 2013 Subsequent Event [Member]	Mar. 31, 2013 Subsequent Event [Member]	Dec. 31, 2012 Subsequent Event [Member]	Sep. 30, 2013 Subsequent Event [Member]	Dec. 31, 2012 Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared, per share	$ 0.09	$ 0.13	$ 0.29	$ 0.40	$ 0.09	$ 0.09	$ 0.09	$ 0.09
Distributions paid to common stock shareholders, per share									$ 0.27	$ 0.38