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	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	$ 242,975
Available-for-sale Securities, Gross Unrealized Gains	5,517
Available-for-sale Securities, Gross Unrealized Losses	1,650
Available-for-sale securities, Estimated Fair Value	246,842us-gaap_AvailableForSaleSecurities	254,746us-gaap_AvailableForSaleSecurities
Held-to-Maturity, Amortized Cost	7,829
Held-to-maturity Securities, Gross Unrealized Gains	1,556
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	9,385
Obligations of U.S. Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	21,664
Available-for-sale Securities, Gross Unrealized Gains	248
Available-for-sale Securities, Gross Unrealized Losses	8
Available-for-sale securities, Estimated Fair Value	21,904
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	98,483
Available-for-sale Securities, Gross Unrealized Gains	3,021
Available-for-sale Securities, Gross Unrealized Losses	67
Available-for-sale securities, Estimated Fair Value	101,437
Held-to-Maturity, Amortized Cost	6,000
Held-to-maturity Securities, Gross Unrealized Gains	1,504
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	7,504
Mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	91,736
Available-for-sale Securities, Gross Unrealized Gains	2,007
Available-for-sale Securities, Gross Unrealized Losses	51
Available-for-sale securities, Estimated Fair Value	93,692
Held-to-Maturity, Amortized Cost	1,829
Held-to-maturity Securities, Gross Unrealized Gains	52
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	1,881
Corporate obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	29,837
Available-for-sale Securities, Gross Unrealized Gains	241
Available-for-sale Securities, Gross Unrealized Losses	1,238
Available-for-sale securities, Estimated Fair Value	28,840
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	1,255
Available-for-sale Securities, Gross Unrealized Gains	0
Available-for-sale Securities, Gross Unrealized Losses	286
Available-for-sale securities, Estimated Fair Value	$ 969

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

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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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