Investment Securities - Proceeds from Sale, Gross Gains (Losses) Realized on Sales, Maturities and Other-Than-Temporary Impairment Charges Related to Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 0	$ 0
Sales Transactions:
Gross gains	0	0
Gross losses	0	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	0	0
Maturities and impairment
Gross Gains	105	0
Gross Losses	0	0
Other Than Temporary Impairment	0	0
Gain Losses Maturities And Impairment	105	0
Net gains and impairment	$ 105	$ 0