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	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 132,868	$ 671
Sales Transactions:
Gross gains	489	233
Gross losses	(441)	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	48	233
Maturities and impairment
Gross Gains	2	4
Gross Losses	0	0
Other Than Temporary Impairment	0	0
Gain Losses Maturities And Impairment	2	4
Net gains and impairment	$ 50	$ 237