Fair Value Measurement of Assets and Liabilities - Schedule of Quantitative Information about Level 3 Inputs Used to Measure Fair Value of Available for Sale Securities (Detail) (Significant Unobservable Inputs (Level 3) [Member], Residential Mortgage-Backed Securities [Member])	3 Months Ended
	Mar. 31, 2015
Fair Value Assets Measured On Recurring Basis [Line Items]
Valuation technique to measure fair value	Discounted cash flow
Prepayment rate, Weighted Average of unobservable inputs	11.10%
Default rate, Weighted Average of unobservable inputs	10.10%
Loss severity, Weighted Average of unobservable inputs	57.10%
Minimum [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs	0.00%
Default rate, Range of unobservable inputs	3.00%
Loss severity, Range of unobservable inputs	40.00%
Maximum [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs	18.20%
Default rate, Range of unobservable inputs	24.90%
Loss severity, Range of unobservable inputs	62.90%