Summary of Amortized Cost and Estimated Fair Value of Available-For-Sale Securities and Held-To-Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	$ 229,080
Available-for-Sale, Gross Unrealized Gains	6,380
Available-for-Sale, Gross Unrealized Losses	1,839
Available-for-sale securities, Estimated Fair Value	233,621	212,529
Held-to-Maturity, Amortized Cost	8,478
Held-to-Maturity, Gross Unrealized Gains	1,518
Held-to-Maturity, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	9,996
Mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	62,766
Available-for-Sale, Gross Unrealized Gains	1,809
Available-for-Sale, Gross Unrealized Losses	18
Available-for-sale securities, Estimated Fair Value	64,557
Held-to-Maturity, Amortized Cost	2,478
Held-to-Maturity, Gross Unrealized Gains	94
Held-to-Maturity, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	2,572
Tax-exempt and taxable obligations of states and municipal subdivisions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	95,832
Available-for-Sale, Gross Unrealized Gains	3,976
Available-for-Sale, Gross Unrealized Losses	25
Available-for-sale securities, Estimated Fair Value	99,783
Held-to-Maturity, Amortized Cost	6,000
Held-to-Maturity, Gross Unrealized Gains	1,424
Held-to-Maturity, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	7,424
Obligations of U.S. Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	46,421
Available-for-Sale, Gross Unrealized Gains	297
Available-for-Sale, Gross Unrealized Losses	6
Available-for-sale securities, Estimated Fair Value	46,712
Corporate obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	22,806
Available-for-Sale, Gross Unrealized Gains	298
Available-for-Sale, Gross Unrealized Losses	1,508
Available-for-sale securities, Estimated Fair Value	21,596
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	1,255
Available-for-Sale, Gross Unrealized Gains	0
Available-for-Sale, Gross Unrealized Losses	282
Available-for-sale securities, Estimated Fair Value	$ 973

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

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details