Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 314,662	$ 336,710	$ 362,945
Gross Unrealized Gains	10,763	11,166	9,771
Gross Unrealized Losses	(1,396)	(967)	(925)
Fair Value	324,029	346,909	371,791
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,000	6,605	28,634
Gross Unrealized Gains	15	271	258
Gross Unrealized Losses		(6)	(44)
Fair Value	5,015	6,870	28,848
State, county and municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	110,628	109,736	78,440
Gross Unrealized Gains	5,051	4,864	3,723
Gross Unrealized Losses	(147)	(210)	(166)
Fair Value	115,532	114,390	81,997
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,542	10,545	11,639
Gross Unrealized Gains	355	330	217
Gross Unrealized Losses	(600)	(547)	(471)
Fair Value	10,297	10,328	11,385
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	188,492	209,824	244,232
Gross Unrealized Gains	5,342	5,701	5,573
Gross Unrealized Losses	(649)	(204)	(244)
Fair Value	$ 193,185	$ 215,321	$ 249,561

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details