Fair Value - Quantitative Information about Significant Unobservable Inputs Used in Fair Value Measurements (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2013
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage Of Adjusted Specific Issuer Evaluation Defaults	50.00%
Percentage of adjusted specific issuer evaluation recoveries	25.00%
Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage Of Adjusted Specific Issuer Evaluation Defaults	0.00%
Minimum [Member] | Pooled Trust Preferred Securities Group 1 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of adjusted specific issuer evaluation recoveries	0.00%
Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage Of Adjusted Specific Issuer Evaluation Defaults	100.00%
Maximum [Member] | Pooled Trust Preferred Securities Group 1 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of adjusted specific issuer evaluation recoveries	100.00%