Single-family properties - Additional Information (Detail) (USD $)					3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Recorded Deed of Trust Not Received [Member]	Dec. 31, 2012 Recorded Deed of Trust Not Received [Member]	Jun. 30, 2013 Single-Family Properties [Member]	Jun. 30, 2012 Single-Family Properties [Member]	Jun. 30, 2013 Single-Family Properties [Member]	Jun. 30, 2012 Single-Family Properties [Member]
Property Subject to or Available for Operating Lease [Line Items]
Net book value	$ 3,039,504,000	$ 505,713,000	$ 208,156,000	$ 131,819,000
Depreciation expense					$ 8,972,000	$ 77,000	$ 11,877,000	$ 102,000