Subsequent events - Additional Information (Detail) (USD $)	9 Months Ended	1 Months Ended					0 Months Ended	1 Months Ended		0 Months Ended
	Sep. 30, 2013	Aug. 31, 2013 Class A Common Shares [Member]	Oct. 25, 2013 Subsequent Events [Member]	Oct. 31, 2013 Subsequent Events [Member] Property	Nov. 08, 2013 Subsequent Events [Member]	Oct. 31, 2013 Subsequent Events [Member] Preferred Offering [Member]	Nov. 07, 2013 Subsequent Events [Member] 5% Series A Participating Preferred Shares [Member]	Oct. 25, 2013 Subsequent Events [Member] 5% Series A Participating Preferred Shares [Member]	Nov. 08, 2013 Subsequent Events [Member] 5% Series A Participating Preferred Shares [Member]	Nov. 07, 2013 Subsequent Events [Member] Class A Common Shares [Member]
Subsequent Event [Line Items]
Number of properties acquired				600
Aggregate purchase price of properties acquired				$ 79,260,000
Proceeds from offering before fees			110,000,000		16,500,000
Underwriting discounts and estimated offering costs			6,204,000		825,000
Sale of stock, number of shares issued		55,422,794						4,400,000	660,000
Preferred shares dividend rate								5.00%	5.00%
Credit facility, additional borrowings, amount				122,000,000
Credit facility, repayment, amount	806,000,000			140,000,000		95,000,000
Credit facility, amount outstanding						$ 220,000,000
Quarterly distribution per common share										$ 0.05
Quarterly distribution, payable date							Dec. 31, 2013			Jan. 10, 2014
Quarterly distribution, record date							Dec. 15, 2013			Dec. 15, 2013
Quarterly dividend per share on Preferred Shares							$ 0.229167