Mortgage Banking Activities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Entity	Sep. 30, 2012
Mortgage Servicing Rights [Line Items]
Residential loans transferred to securitization entities	$ 1,210,000,000		$ 5,250,000,000
MSRs at a taxable REIT subsidiary	13,000,000		41,128,000	3,849,000
Purchase of mortgage servicing rights	3,106,000		3,106,000
Mortgage Servicing Rights
Mortgage Servicing Rights [Line Items]
MSRs at a taxable REIT subsidiary	16,677,000	1,241,000	45,291,000	3,849,000
Number of securitization entities to which asset transferred			11
Rights acquired and retained to service, original loans transferred	1,190,000,000		4,530,000,000
Principal balance of residential loans for which servicing rights owned	5,580,000,000		5,580,000,000
Amount of MSRs loans sold to third parties	1,000,000		72,000,000
Principal balance of conforming loans acquired	$ 307,000,000		$ 307,000,000