Investment Securities - Age of Unrealized Losses and Fair Value of Related Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	$ 49,439	$ 559,333
Less than Twelve Months, Unrealized Losses	(1,157)	(38,574)
More than Twelve Months, Fair Value	498,377	56,475
More than Twelve Months, Unrealized Losses	(20,122)	(7,688)
Total, Fair Value	547,816	615,808
Total, Unrealized Losses	(21,279)	(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	91,887	0
More than Twelve Months, Unrealized Losses	(7,944)	0
Total, Fair Value	91,887	84,665
Total, Unrealized Losses	(7,944)	(15,170)
U.S. Government Agency Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	0	26,402
Less than Twelve Months, Unrealized Losses	0	(703)
More than Twelve Months, Fair Value	20,892	0
More than Twelve Months, Unrealized Losses	(312)	0
Total, Fair Value	20,892	26,402
Total, Unrealized Losses	(312)	(703)
Obligations of States and State Agencies [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	0	10,598
Less than Twelve Months, Unrealized Losses	0	(798)
More than Twelve Months, Fair Value	10,956	0
More than Twelve Months, Unrealized Losses	(322)	0
Total, Fair Value	10,956	10,598
Total, Unrealized Losses	(322)	(798)
Municipal Bonds [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	10,781	13,461
Less than Twelve Months, Unrealized Losses	(473)	(1,365)
More than Twelve Months, Fair Value	14,575	0
More than Twelve Months, Unrealized Losses	(219)	0
Total, Fair Value	25,356	13,461
Total, Unrealized Losses	(692)	(1,365)
Obligations of States and Political Subdivisions [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	10,781	24,059
Less than Twelve Months, Unrealized Losses	(473)	(2,163)
More than Twelve Months, Fair Value	25,531	0
More than Twelve Months, Unrealized Losses	(541)	0
Total, Fair Value	36,312	24,059
Total, Unrealized Losses	(1,014)	(2,163)
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	27,250	368,306
Less than Twelve Months, Unrealized Losses	(658)	(18,434)
More than Twelve Months, Fair Value	300,710	24,734
More than Twelve Months, Unrealized Losses	(7,230)	(2,285)
Total, Fair Value	327,960	393,040
Total, Unrealized Losses	(7,888)	(20,719)
Trust Preferred Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	850	2,024
Less than Twelve Months, Unrealized Losses	(1)	(25)
More than Twelve Months, Fair Value	15,351	15,022
More than Twelve Months, Unrealized Losses	(2,935)	(4,206)
Total, Fair Value	16,201	17,046
Total, Unrealized Losses	(2,936)	(4,231)
Corporate and Other Debt Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	10,512	53,654
Less than Twelve Months, Unrealized Losses	(23)	(2,073)
More than Twelve Months, Fair Value	28,943	2,471
More than Twelve Months, Unrealized Losses	(578)	(30)
Total, Fair Value	39,455	56,125
Total, Unrealized Losses	(601)	(2,103)
Equity Securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	46	223
Less than Twelve Months, Unrealized Losses	(2)	(6)
More than Twelve Months, Fair Value	15,063	14,248
More than Twelve Months, Unrealized Losses	(582)	(1,167)
Total, Fair Value	15,109	14,471
Total, Unrealized Losses	$ (584)	$ (1,173)