Investment Securities - Age of Unrealized Losses and Fair Value of Related Securities Held to Maturity (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	$ 374,643,000	$ 97,569,000
Less than Twelve Months, Unrealized Losses	(4,118,000)	(7,563,000)
More than Twelve Months, Fair Value	63,882,000	79,948,000
More than Twelve Months, Unrealized Losses	(15,361,000)	(42,182,000)
Total, Fair Value	438,525,000	177,517,000
Total, Unrealized Losses	(19,479,000)	(49,745,000)
U.S. Treasury securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	97,625,000
Less than Twelve Months, Unrealized Losses	(2,218,000)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value	97,625,000
Total, Unrealized Losses	(2,218,000)
Residential mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	269,895,000	41,673,000
Less than Twelve Months, Unrealized Losses	(1,256,000)	(1,655,000)
More than Twelve Months, Fair Value	21,089,000	22,639,000
More than Twelve Months, Unrealized Losses	(2,103,000)	(3,789,000)
Total, Fair Value	290,984,000	64,312,000
Total, Unrealized Losses	(3,359,000)	(5,444,000)
Trust preferred securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	760,000	23,962,000
Less than Twelve Months, Unrealized Losses	(511,000)	(1,061,000)
More than Twelve Months, Fair Value	27,865,000	44,758,000
More than Twelve Months, Unrealized Losses	(11,228,000)	(35,524,000)
Total, Fair Value	28,625,000	68,720,000
Total, Unrealized Losses	(11,739,000)	(36,585,000)
Corporate and other debt securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	5,394,000	3,243,000
Less than Twelve Months, Unrealized Losses	(58,000)	(173,000)
More than Twelve Months, Fair Value	2,264,000
More than Twelve Months, Unrealized Losses	(236,000)
Total, Fair Value	7,658,000	3,243,000
Total, Unrealized Losses	(294,000)	(173,000)
Equity securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	969,000	20,570,000
Less than Twelve Months, Unrealized Losses	(75,000)	(4,430,000)
More than Twelve Months, Fair Value	12,664,000	12,551,000
More than Twelve Months, Unrealized Losses	(1,794,000)	(2,869,000)
Total, Fair Value	13,633,000	33,121,000
Total, Unrealized Losses	(1,869,000)	(7,299,000)
U.S. government agency securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value		7,980,000
Less than Twelve Months, Unrealized Losses		(243,000)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value		7,980,000
Total, Unrealized Losses		(243,000)
Obligations of states and political subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value		141,000
Less than Twelve Months, Unrealized Losses		(1,000)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total, Fair Value		141,000
Total, Unrealized Losses		$ (1,000)