Investment Securities - Age of Unrealized Losses and Fair Value of Related Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	$ 710,652	$ 124,360
Less than Twelve Months, Unrealized Losses	(39,085)	(760)
More than Twelve Months, Fair Value	57,806	48,802
More than Twelve Months, Unrealized Losses	(12,187)	(14,570)
Total, Fair Value	768,458	173,162
Total, Unrealized Losses	(51,272)	(15,330)
U.S. Treasury securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	64,537
Less than Twelve Months, Unrealized Losses	(515)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value	64,537
Total, Unrealized Losses	(515)
U.S. government agency securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	4,365
Less than Twelve Months, Unrealized Losses	(62)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value	4,365
Total, Unrealized Losses	(62)
Obligations of states and state agencies [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	80,612	7,463
Less than Twelve Months, Unrealized Losses	(5,473)	(105)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value	80,612	7,463
Total, Unrealized Losses	(5,473)	(105)
Municipal bonds [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	85,988	8,055
Less than Twelve Months, Unrealized Losses	(5,154)	(92)
More than Twelve Months, Fair Value	1,326
More than Twelve Months, Unrealized Losses	(105)
Total, Fair Value	87,314	8,055
Total, Unrealized Losses	(5,259)	(92)
Obligations of states and political subdivisions [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	166,600	15,518
Less than Twelve Months, Unrealized Losses	(10,627)	(197)
More than Twelve Months, Fair Value	1,326
More than Twelve Months, Unrealized Losses	(105)
Total, Fair Value	167,926	15,518
Total, Unrealized Losses	(10,732)	(197)
Residential mortgage-backed securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	465,400	80,152
Less than Twelve Months, Unrealized Losses	(27,631)	(355)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value	465,400	80,152
Total, Unrealized Losses	(27,631)	(355)
Trust preferred securities [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Less than Twelve Months, Fair Value	9,750	28,690
Less than Twelve Months, Unrealized Losses	(250)	(208)
More than Twelve Months, Fair Value	56,480	48,802
More than Twelve Months, Unrealized Losses	(12,082)	(14,570)
Total, Fair Value	66,230	77,492
Total, Unrealized Losses	$ (12,332)	$ (14,778)