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	9 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	$ 253,804
Available-for-sale Securities, Gross Unrealized Gain	3,030
Available-for-sale Securities, Gross Unrealized Loss	5,021
Available-for-sale securities, Estimated Fair Value	251,813	214,393
Held-to-Maturity, Amortized Cost	8,446
Held-to-maturity Securities, Gross Unrecognized Gain	1,061
Held-to-maturity Securities, Gross Unrecognized Loss	66
Held-to-Maturity, Estimated Fair Value	9,441
Obligations of U.S. Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	32,573
Available-for-sale Securities, Gross Unrealized Gain	84
Available-for-sale Securities, Gross Unrealized Loss	130
Available-for-sale securities, Estimated Fair Value	32,527
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	110,052
Available-for-sale Securities, Gross Unrealized Gain	1,842
Available-for-sale Securities, Gross Unrealized Loss	1,527
Available-for-sale securities, Estimated Fair Value	110,367
Held-to-Maturity, Amortized Cost	6,000
Held-to-maturity Securities, Gross Unrecognized Gain	1,061
Held-to-maturity Securities, Gross Unrecognized Loss	0
Held-to-Maturity, Estimated Fair Value	7,061
Mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	81,526
Available-for-sale Securities, Gross Unrealized Gain	871
Available-for-sale Securities, Gross Unrealized Loss	1,365
Available-for-sale securities, Estimated Fair Value	81,032
Held-to-Maturity, Amortized Cost	2,446
Held-to-maturity Securities, Gross Unrecognized Gain	0
Held-to-maturity Securities, Gross Unrecognized Loss	66
Held-to-Maturity, Estimated Fair Value	2,380
Corporate obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	28,398
Available-for-sale Securities, Gross Unrealized Gain	233
Available-for-sale Securities, Gross Unrealized Loss	1,713
Available-for-sale securities, Estimated Fair Value	26,918
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	1,255
Available-for-sale Securities, Gross Unrealized Gain	0
Available-for-sale Securities, Gross Unrealized Loss	286
Available-for-sale securities, Estimated Fair Value	$ 969

Held to maturity Securities, Amortized Cost

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

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of unrecognized gain before loss on investments in held-to-maturity securities.

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Amount of unrecognized loss before gain on investments in held-to-maturity securities. Excludes write-down for other than temporary impairment (OTTI).

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