Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 795,545	$ 866,904
Gross Unrealized Gains	8,939	9,050
Gross Unrealized Losses	(21,279)	(46,262)
Fair Value	783,205	829,692
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,831	99,835
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,944)	(15,170)
Fair Value	91,887	84,665
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,557	48,407
Gross Unrealized Gains	796	923
Gross Unrealized Losses	(312)	(703)
Fair Value	46,041	48,627
Obligations of States and State Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,278	11,441
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(322)	(798)
Fair Value	10,956	10,643
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,656	27,671
Gross Unrealized Gains	95	751
Gross Unrealized Losses	(692)	(1,365)
Fair Value	27,059	27,057
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,934	39,112
Gross Unrealized Gains	95	751
Gross Unrealized Losses	(1,014)	(2,163)
Fair Value	38,015	37,700
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	481,781	524,781
Gross Unrealized Gains	4,239	3,967
Gross Unrealized Losses	(7,888)	(20,719)
Fair Value	478,132	508,029
Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,263	23,333
Gross Unrealized Gains	323	113
Gross Unrealized Losses	(2,936)	(4,231)
Fair Value	20,650	19,215
Corporate and Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	83,108	83,819
Gross Unrealized Gains	2,029	1,682
Gross Unrealized Losses	(601)	(2,103)
Fair Value	84,536	83,398
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,071	47,617
Gross Unrealized Gains	1,457	1,614
Gross Unrealized Losses	(584)	(1,173)
Fair Value	$ 23,944	$ 48,058