Single-family properties - Additional Information (Detail) (USD $)			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Single-Family Properties [Member]	Sep. 30, 2012 Single-Family Properties [Member]	Sep. 30, 2013 Single-Family Properties [Member]	Sep. 30, 2012 Single-Family Properties [Member]	Sep. 30, 2013 Recorded Deed of Trust Not Received [Member]	Dec. 31, 2012 Recorded Deed of Trust Not Received [Member]
Property Subject to or Available for Operating Lease [Line Items]
Net book value	$ 3,530,122,000	$ 505,713,000					$ 95,447,000	$ 131,819,000
Depreciation expense			$ 20,841,000	$ 490,000	$ 32,718,000	$ 592,000