Investment Securities - Age of Unrealized Losses and Fair Value of Related Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	$ 395,350	$ 559,333
Less than Twelve Months, Unrealized Losses	(13,340)	(38,574)
More than Twelve Months, Fair Value	208,124	56,475
More than Twelve Months, Unrealized Losses	(19,925)	(7,688)
Total, Fair Value	603,474	615,808
Total, Unrealized Losses	(33,265)	(46,262)
U.S. Treasury Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	0	84,665
Less than Twelve Months, Unrealized Losses	0	(15,170)
More than Twelve Months, Fair Value	88,871	0
More than Twelve Months, Unrealized Losses	(10,962)	0
Total, Fair Value	88,871	84,665
Total, Unrealized Losses	(10,962)	(15,170)
U.S. Government Agency Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	20,834	26,402
Less than Twelve Months, Unrealized Losses	(453)	(703)
More than Twelve Months, Fair Value	0	0
More than Twelve Months, Unrealized Losses	0	0
Total, Fair Value	20,834	26,402
Total, Unrealized Losses	(453)	(703)
Obligations of States and State Agencies [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	10,822	10,598
Less than Twelve Months, Unrealized Losses	(516)	(798)
More than Twelve Months, Fair Value	0	0
More than Twelve Months, Unrealized Losses	0	0
Total, Fair Value	10,822	10,598
Total, Unrealized Losses	(516)	(798)
Municipal Bonds [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	25,293	13,461
Less than Twelve Months, Unrealized Losses	(761)	(1,365)
More than Twelve Months, Fair Value	0	0
More than Twelve Months, Unrealized Losses	0	0
Total, Fair Value	25,293	13,461
Total, Unrealized Losses	(761)	(1,365)
Obligations of States and Political Subdivisions [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	36,115	24,059
Less than Twelve Months, Unrealized Losses	(1,277)	(2,163)
More than Twelve Months, Fair Value	0	0
More than Twelve Months, Unrealized Losses	0	0
Total, Fair Value	36,115	24,059
Total, Unrealized Losses	(1,277)	(2,163)
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	305,171	368,306
Less than Twelve Months, Unrealized Losses	(10,525)	(18,434)
More than Twelve Months, Fair Value	75,789	24,734
More than Twelve Months, Unrealized Losses	(3,740)	(2,285)
Total, Fair Value	380,960	393,040
Total, Unrealized Losses	(14,265)	(20,719)
Trust Preferred Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	788	2,024
Less than Twelve Months, Unrealized Losses	(5)	(25)
More than Twelve Months, Fair Value	15,298	15,022
More than Twelve Months, Unrealized Losses	(3,885)	(4,206)
Total, Fair Value	16,086	17,046
Total, Unrealized Losses	(3,890)	(4,231)
Corporate and Other Debt Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	32,168	53,654
Less than Twelve Months, Unrealized Losses	(1,074)	(2,073)
More than Twelve Months, Fair Value	13,896	2,471
More than Twelve Months, Unrealized Losses	(193)	(30)
Total, Fair Value	46,064	56,125
Total, Unrealized Losses	(1,267)	(2,103)
Equity Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	274	223
Less than Twelve Months, Unrealized Losses	(6)	(6)
More than Twelve Months, Fair Value	14,270	14,248
More than Twelve Months, Unrealized Losses	(1,145)	(1,167)
Total, Fair Value	14,544	14,471
Total, Unrealized Losses	$ (1,151)	$ (1,173)