Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Securities available-for-sale, at fair value	$ 660,963,000	$ 640,273,000
U.S. Treasury securities
ASSETS
Securities available-for-sale, at fair value	14,941,000	14,880,000
Obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	263,303,000	269,285,000
Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	128,835,000	118,006,000
Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	40,125,000	46,668,000
Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	69,204,000	39,673,000
Obligations of states and political subdivisions
ASSETS
Securities available-for-sale, at fair value	134,886,000	142,702,000
Marketable equity securities
ASSETS
Securities available-for-sale, at fair value	9,669,000	9,059,000
Level 3
LIABILITIES
Total Liabilities		0
Fair Value Measurements, Recurring
ASSETS
Securities available-for-sale, at fair value	660,963,000	640,273,000
Trading securities held in a Rabbi Trust	4,021,000	3,456,000
Total securities	664,984,000	643,729,000
Total Assets	676,540,000	656,945,000
LIABILITIES
Total Liabilities	11,281,000	13,010,000
Fair Value Measurements, Recurring | U.S. Treasury securities
ASSETS
Securities available-for-sale, at fair value	14,941,000	14,880,000
Fair Value Measurements, Recurring | Obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	263,303,000	269,285,000
Fair Value Measurements, Recurring | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	128,835,000	118,006,000
Fair Value Measurements, Recurring | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	40,125,000	46,668,000
Fair Value Measurements, Recurring | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	69,204,000	39,673,000
Fair Value Measurements, Recurring | Obligations of states and political subdivisions
ASSETS
Securities available-for-sale, at fair value	134,886,000	142,702,000
Fair Value Measurements, Recurring | Marketable equity securities
ASSETS
Securities available-for-sale, at fair value	9,669,000	9,059,000
Fair Value Measurements, Recurring | Interest Rate Swap
ASSETS
Derivative financial assets	11,295,000	12,981,000
LIABILITIES
Derivative financial liabilities	11,276,000	12,953,000
Fair Value Measurements, Recurring | Interest Rate Lock Commitments
ASSETS
Derivative financial assets	261,000	235,000
Fair Value Measurements, Recurring | Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	5,000	57,000
Fair Value Measurements, Recurring | Level 1
ASSETS
Securities available-for-sale, at fair value		178,000
Trading securities held in a Rabbi Trust	4,021,000	3,456,000
Total securities	4,021,000	3,634,000
Total Assets	4,021,000	3,634,000
Fair Value Measurements, Recurring | Level 1 | U.S. Treasury securities
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Obligations of states and political subdivisions
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 1 | Marketable equity securities
ASSETS
Securities available-for-sale, at fair value	0	178,000
Fair Value Measurements, Recurring | Level 1 | Interest Rate Swap
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring | Level 1 | Interest Rate Lock Commitments
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring | Level 1 | Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring | Level 2
ASSETS
Securities available-for-sale, at fair value	660,963,000	640,095,000
Trading securities held in a Rabbi Trust	0	0
Total securities	660,963,000	640,095,000
Total Assets	672,519,000	653,311,000
LIABILITIES
Total Liabilities	11,281,000	13,010,000
Fair Value Measurements, Recurring | Level 2 | U.S. Treasury securities
ASSETS
Securities available-for-sale, at fair value	14,941,000	14,880,000
Fair Value Measurements, Recurring | Level 2 | Obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	263,303,000	269,285,000
Fair Value Measurements, Recurring | Level 2 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	128,835,000	118,006,000
Fair Value Measurements, Recurring | Level 2 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	40,125,000	46,668,000
Fair Value Measurements, Recurring | Level 2 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	69,204,000	39,673,000
Fair Value Measurements, Recurring | Level 2 | Obligations of states and political subdivisions
ASSETS
Securities available-for-sale, at fair value	134,886,000	142,702,000
Fair Value Measurements, Recurring | Level 2 | Marketable equity securities
ASSETS
Securities available-for-sale, at fair value	9,669,000	8,881,000
Fair Value Measurements, Recurring | Level 2 | Interest Rate Swap
ASSETS
Derivative financial assets	11,295,000	12,981,000
LIABILITIES
Derivative financial liabilities	11,276,000	12,953,000
Fair Value Measurements, Recurring | Level 2 | Interest Rate Lock Commitments
ASSETS
Derivative financial assets	261,000	235,000
Fair Value Measurements, Recurring | Level 2 | Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	5,000	57,000
Fair Value Measurements, Recurring | Level 3
ASSETS
Trading securities held in a Rabbi Trust	0	0
Fair Value Measurements, Recurring | Level 3 | U.S. Treasury securities
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Obligations of states and political subdivisions
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Marketable equity securities
ASSETS
Securities available-for-sale, at fair value	0	0
Fair Value Measurements, Recurring | Level 3 | Interest Rate Swap
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring | Level 3 | Interest Rate Lock Commitments
ASSETS
Derivative financial assets	0	$ 0
Fair Value Measurements, Recurring | Level 3 | Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	$ 0