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) (Residential mortgage-backed securities [Member])	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2014
Fair Value Assets Measured On Recurring Basis [Line Items]
Valuation technique to measure fair value		Discounted cash flow
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Weighted Average of unobservable inputs		12.90%
Default rate, Weighted Average of unobservable inputs		8.70%
Loss severity, Weighted Average of unobservable inputs		56.50%
Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs		0.20%
Default rate, Range of unobservable inputs	3.00%
Loss severity, Range of unobservable inputs		41.30%
Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs		19.80%
Default rate, Range of unobservable inputs		21.60%
Loss severity, Range of unobservable inputs	62.00%