Five Largest Geographic Concentrations of Residential Loans (Detail) (Geographic Concentration Risk, Residential Mortgage)	6 Months Ended
	Jun. 30, 2013
Concentration Risk [Line Items]
Concentration risk percentage	100.00%
California
Concentration Risk [Line Items]
Concentration risk percentage	49.70%
Illinois
Concentration Risk [Line Items]
Concentration risk percentage	5.80%
Massachusetts
Concentration Risk [Line Items]
Concentration risk percentage	5.80%
Virginia
Concentration Risk [Line Items]
Concentration risk percentage	4.20%
Maryland
Concentration Risk [Line Items]
Concentration risk percentage	4.20%
Other states (none greater than 4%)
Concentration Risk [Line Items]
Concentration risk percentage	30.30%