Summary of Amortized Cost and Estimated Fair Value of Available-For-Sale Securities and Held-To-Maturity Securities (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	$ 235,744
Available-for-sale Securities, Gross Unrealized Gains	3,235
Available-for-sale Securities, Gross Unrealized Losses	2,503
Available-for-sale securities, Estimated Fair Value	236,476	$ 254,746
Held-to-Maturity, Amortized Cost	7,651
Held-to-maturity Securities, Gross Unrealized Gains	1,320
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	8,971
Obligations of U.S. Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	20,057
Available-for-sale Securities, Gross Unrealized Gains	105
Available-for-sale Securities, Gross Unrealized Losses	13
Available-for-sale securities, Estimated Fair Value	20,149
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	94,656
Available-for-sale Securities, Gross Unrealized Gains	1,805
Available-for-sale Securities, Gross Unrealized Losses	538
Available-for-sale securities, Estimated Fair Value	95,923
Held-to-Maturity, Amortized Cost	6,000
Held-to-maturity Securities, Gross Unrealized Gains	1,306
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	7,306
Mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	92,862
Available-for-sale Securities, Gross Unrealized Gains	1,195
Available-for-sale Securities, Gross Unrealized Losses	434
Available-for-sale securities, Estimated Fair Value	93,623
Held-to-Maturity, Amortized Cost	1,651
Held-to-maturity Securities, Gross Unrealized Gains	14
Held-to-maturity Securities, Gross Unrealized Losses	0
Held-to-Maturity, Estimated Fair Value	1,665
Corporate obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale, Amortized Cost	26,914
Available-for-sale Securities, Gross Unrealized Gains	130
Available-for-sale Securities, Gross Unrealized Losses	1,232
Available-for-sale securities, Estimated Fair Value	25,812
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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