Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 771,375	$ 866,904
Gross Unrealized Gains	8,212	9,050
Gross Unrealized Losses	(21,166)	(46,262)
Fair Value	758,421	829,692
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,829	99,835
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6,833)	(15,170)
Fair Value	92,996	84,665
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,504	48,407
Gross Unrealized Gains	756	923
Gross Unrealized Losses	(246)	(703)
Fair Value	45,014	48,627
Obligations of States and State Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,220	11,441
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(108)	(798)
Fair Value	11,112	10,643
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,018	27,671
Gross Unrealized Gains	92	751
Gross Unrealized Losses	(607)	(1,365)
Fair Value	26,503	27,057
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,238	39,112
Gross Unrealized Gains	92	751
Gross Unrealized Losses	(715)	(2,163)
Fair Value	37,615	37,700
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	465,092	524,781
Gross Unrealized Gains	3,852	3,967
Gross Unrealized Losses	(9,367)	(20,719)
Fair Value	459,577	508,029
Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,228	23,333
Gross Unrealized Gains	430	113
Gross Unrealized Losses	(2,414)	(4,231)
Fair Value	21,244	19,215
Corporate and Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	77,413	83,819
Gross Unrealized Gains	1,506	1,682
Gross Unrealized Losses	(1,004)	(2,103)
Fair Value	77,915	83,398
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,071	47,617
Gross Unrealized Gains	1,576	1,614
Gross Unrealized Losses	(587)	(1,173)
Fair Value	$ 24,060	$ 48,058