Investment Securities (Detail) - Information regarding the CDO portfolio characteristics and OTTI losses (Collateralized Debt Obligations [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011
PRETZL XIV [Member]
Credit rating	C	C	C
Rating agency	Fitch	Fitch	Fitch
Percentage in deferral or default	36.66%	39.14%	36.66%
Constant default rate - high	1.23%	0.52%	1.13%
Constant default rate - low	0.25%	0.25%	0.25%
Discount margin	11.57%	11.57%	11.57%
USCAP II [Member]
Credit rating	C	C	C
Rating agency	Fitch	Fitch	Fitch
Percentage in deferral or default	21.18%	25.24%	21.18%
Constant default rate - high	1.12%	0.35%	0.69%
Constant default rate - low	0.25%	0.25%	0.25%
Discount margin	11.65%	11.65%	11.65%