Age of Unrealized Losses and Fair Value of Related Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	$ 57,430	$ 85,657
Less than Twelve Months, Unrealized Losses	(231)	(1,087)
More than Twelve Months, Fair Value	80,119	63,222
More than Twelve Months, Unrealized Losses	(17,139)	(23,552)
Total Fair Value	137,549	148,879
Total, Unrealized Losses	(17,370)	(24,639)
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	11,653	1,854
Less than Twelve Months, Unrealized Losses	(77)	(13)
More than Twelve Months, Fair Value		50
More than Twelve Months, Unrealized Losses		(1)
Total Fair Value	11,653	1,904
Total, Unrealized Losses	(77)	(14)
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	35,959	33,520
Less than Twelve Months, Unrealized Losses	(117)	(152)
More than Twelve Months, Fair Value
More than Twelve Months, Unrealized Losses
Total Fair Value	35,959	33,520
Total, Unrealized Losses	(117)	(152)
Trust preferred securities
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value	9,818	35,527
Less than Twelve Months, Unrealized Losses	(37)	(730)
More than Twelve Months, Fair Value	80,119	55,612
More than Twelve Months, Unrealized Losses	(17,139)	(22,137)
Total Fair Value	89,937	91,139
Total, Unrealized Losses	(17,176)	(22,867)
Corporate and other debt securities
Schedule of Held-to-maturity Securities [Line Items]
Less than Twelve Months, Fair Value		14,756
Less than Twelve Months, Unrealized Losses		(192)
More than Twelve Months, Fair Value		7,560
More than Twelve Months, Unrealized Losses		(1,414)
Total Fair Value		22,316
Total, Unrealized Losses		$ (1,606)