Securities Available-for-Sale - Amortized Cost and Fair Value of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 579,626	$ 510,399
Fair Value	588,488	509,425
Obligations of U.S. Government Corporations and Agencies, and Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	24,049
Due after one year through five years, Amortized Cost	182,816
Due after five years through ten years, Amortized Cost	98,068
Due after ten years, Amortized Cost	88,329
Available-for-sale Securities, Debt Maturities, Amortized Cost	393,262
Due in one year or less, Fair Value	24,289
Due after one year through five years, Fair Value	184,074
Due after five years through ten years, Fair Value	99,420
Due after ten years, Fair Value	90,778
Fair Value, Debt securities	398,561
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93,787	63,776
Fair Value	94,604	63,774
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,900	47,934
Fair Value	46,389	48,669
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,098	40,357
Fair Value	39,920	39,052
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	572,047	502,820
Fair Value	579,474	500,510
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,579	7,579
Fair Value	$ 9,014	$ 8,915