Amortized Cost And Corresponding Fair Value Of Investment Securities Available For Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 494,299	$ 513,309
Gross Unrealized Gains	4,659	5,093
Gross Unrealized Losses	1,352	1,189
Estimated Fair Value	497,606	517,213
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	504	507
Gross Unrealized Gains	5	6
Gross Unrealized Losses	0	0
Estimated Fair Value	509	513
Obligations of U.S. Government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	172,834	181,624
Gross Unrealized Gains	1,180	181
Gross Unrealized Losses	161	185
Estimated Fair Value	173,853	181,620
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	880	1,325
Gross Unrealized Gains	2	4
Gross Unrealized Losses	0	0
Estimated Fair Value	882	1,329
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	320,081	329,853
Gross Unrealized Gains	3,472	4,902
Gross Unrealized Losses	1,191	1,004
Estimated Fair Value	$ 322,362	$ 333,751

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