Loans (Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 118,703	$ 136,760	$ 113,515
Recorded Investment	97,626	99,924	84,565
Related Allowance	4,882	8,166	3,904
Commercial And Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	61,081	79,327	57,723
Recorded Investment	49,076	52,970	39,331
Related Allowance	4,059	6,883	2,696
Commercial Real Estate, Buildings, Land And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	54,690	52,193	51,163
Recorded Investment	46,092	42,115	40,929
Related Allowance	823	1,283	1,113
Commercial Real Estate Construction Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	1,515	2,162	1,568
Recorded Investment	1,144	1,773	1,281
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	974	2,510	2,499
Recorded Investment	894	2,498	2,470
Related Allowance			95
Consumer And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	443	568	562
Recorded Investment	420	568	554
Quarter To Date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	89,897	109,976	92,245
Quarter To Date | Commercial And Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	44,140	60,696	46,151
Quarter To Date | Commercial Real Estate, Buildings, Land And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	42,569	44,453	41,522
Quarter To Date | Commercial Real Estate Construction Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,671	2,265	1,527
Quarter To Date | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,087	2,227	2,484
Quarter To Date | Consumer And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	430	335	561
Year To Date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	88,127	115,003	108,914
Year To Date | Commercial And Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	43,087	57,455	53,830
Year To Date | Commercial Real Estate, Buildings, Land And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	41,283	50,562	48,635
Year To Date | Commercial Real Estate Construction Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,465	5,104	4,339
Year To Date | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,805	1,689	1,845
Year To Date | Consumer And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	487	193	265
Recorded Investment With No Allowance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	79,380	81,689	76,952
Recorded Investment With No Allowance | Commercial And Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	37,231	42,583	34,712
Recorded Investment With No Allowance | Commercial Real Estate, Buildings, Land And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	39,691	34,267	38,686
Recorded Investment With No Allowance | Commercial Real Estate Construction Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	1,144	1,773	1,281
Recorded Investment With No Allowance | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	894	2,498	1,719
Recorded Investment With No Allowance | Consumer And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	420	568	554
Recorded Investment With Allowance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	18,246	18,235	7,613
Recorded Investment With Allowance | Commercial And Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	11,845	10,387	4,619
Recorded Investment With Allowance | Commercial Real Estate, Buildings, Land And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,401	7,848	2,243
Recorded Investment With Allowance | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment			$ 751