Shareholders' equity - Additional Information 1 (Detail) (Operating Partnership [Member], USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Series D Convertible Units [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Units outstanding	4,375,000
Stock split conversion ratio	1
Closing price per share	$ 18.00
Series D Convertible Units [Member] | Scenario one, over four consecutive quarters [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Adjusted funds from operations per common share	$ 0.80
Series D Convertible Units [Member] | Scenario two, two consecutive quarters [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Units distribution percentage	70.00%
Series E Convertible Units [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Units outstanding	4,375,000
Stock split conversion ratio	1
Annualized EBITDA Contribution	$ 14
Series E Convertible Units [Member] | Scenario three, measurement period [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
EBITDA contribution	$ 28
Series C Convertible Units [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Percentage of Property Contribution	3.90%
Percentage of scheduled rents	98.00%
Property Contributions price per unit	$ 15.50
Units outstanding	31,085,974