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	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from Sale of Available-for-sale Securities	$ 0	$ 132,868
Sales Transactions:
Gross gains	0	489
Gross losses	0	(441)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	0	48
Maturities and impairment
Gross Gains	125	2
Gross Losses	0	0
Other Than Temporary Impairment	0	0
Gain Losses Maturities And Impairment	125	2
Net gains and impairment	$ 125	$ 50