Investment Securities - Realized Gains and Losses on Sales of Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments Debt And Equity Securities [Abstract]
Gross gains, Sales transactions	$ 1	$ 1,234	$ 3,381	$ 1,374
Gross losses, Sales transactions				(298)
Gains on Sales transactions, net	1	1,234	3,381	1,076
Gross gains, Maturities and other securities transactions	41	6	649	19
Gross losses, Maturities and other securities transactions	(1)	(36)	(31)	(48)
Gains (losses) on Maturities and other securities transactions, net	40	(30)	618	(29)
Total gains on securities transactions, net	$ 41	$ 1,204	$ 3,999	$ 1,047