Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
ASSETS
Total securities available-for-sale	$ 615,657	$ 509,425
US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,803
Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	263,406	234,751
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	111,053	63,774
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	44,581	48,669
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,380	39,052
Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	133,945	114,264
Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,489	8,915
Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	615,657	509,425
Trading securities held in a Rabbi Trust	3,286	2,864
Total securities	618,943	512,289
Total Assets	631,255	526,106
LIABILITIES
Total Liabilities	12,113	13,647
Fair Value Measurements, Recurring [Member] | US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,803	0
Fair Value Measurements, Recurring [Member] | Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	263,406	234,751
Fair Value Measurements, Recurring [Member] | Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	111,053	63,774
Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	44,581	48,669
Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,380	39,052
Fair Value Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	133,945	114,264
Fair Value Measurements, Recurring [Member] | Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,489	8,915
Fair Value Measurements, Recurring [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	12,125	13,698
LIABILITIES
Derivative financial liabilities	12,103	13,647
Fair Value Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	187	85
Fair Value Measurements, Recurring [Member] | Forward Sale Contracts [Member]
ASSETS
Derivative financial assets	0	34
LIABILITIES
Derivative financial liabilities	10
Level 1 [Member] | Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	179	202
Trading securities held in a Rabbi Trust	3,286	2,864
Total securities	3,465	3,066
Total Assets	3,465	3,066
LIABILITIES
Total Liabilities	0
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | US Treasury Securities [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	179	202
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets
LIABILITIES
Derivative financial liabilities
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets
Level 1 [Member] | Fair Value Measurements, Recurring [Member] | Forward Sale Contracts [Member]
ASSETS
Derivative financial assets	0
LIABILITIES
Derivative financial liabilities
Level 2 [Member] | Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	615,478	509,223
Trading securities held in a Rabbi Trust
Total securities	615,478	509,223
Total Assets	627,790	523,040
LIABILITIES
Total Liabilities	12,113	13,647
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,803	0
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	263,406	234,751
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	111,053	63,774
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	44,581	48,669
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,380	39,052
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	133,945	114,264
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,310	8,713
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	12,125	13,698
LIABILITIES
Derivative financial liabilities	12,103	13,647
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	187	85
Level 2 [Member] | Fair Value Measurements, Recurring [Member] | Forward Sale Contracts [Member]
ASSETS
Derivative financial assets	0	34
LIABILITIES
Derivative financial liabilities	10
Level 3 [Member] | Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale
Trading securities held in a Rabbi Trust
Total securities
Total Assets
LIABILITIES
Total Liabilities	0
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | US Treasury Securities [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets
LIABILITIES
Derivative financial liabilities
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets
Level 3 [Member] | Fair Value Measurements, Recurring [Member] | Forward Sale Contracts [Member]
ASSETS
Derivative financial assets	0
LIABILITIES
Derivative financial liabilities