Summary of Significant Valuation Assumptions for Available for Sale Securities (Detail)	Sep. 30, 2013
Residential Prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	4.00%
Loss severity	15.00%
Projected losses	0.00%
Residential Prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	50.00%
Loss severity	56.00%
Projected losses	38.00%
Residential non-prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	3.00%
Loss severity	30.00%
Projected losses	4.00%
Residential non-prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	10.00%
Loss severity	59.00%
Projected losses	15.00%