Analysis of Impaired Loans by Class (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	$ 33,260	$ 34,471
Recorded Investment with No Allowance	11,271	20,935
Recorded Investment with Allowance	14,889	5,374
Total Recorded Investment	26,160	26,309
Related Allowance	3,515	2,174
Average Recorded Investment	26,234	25,995
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	22,285	22,453
Recorded Investment with No Allowance	1,680	12,119
Recorded Investment with Allowance	14,294	2,938
Total Recorded Investment	15,974	15,057
Related Allowance	3,206	1,393
Average Recorded Investment	15,515	13,287
Commercial - credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance
Recorded Investment with No Allowance
Recorded Investment with Allowance
Total Recorded Investment
Related Allowance
Average Recorded Investment
Real estate - construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	1,569	276
Recorded Investment with No Allowance	1,219	276
Recorded Investment with Allowance	123
Total Recorded Investment	1,342	276
Related Allowance	64
Average Recorded Investment	1,346	118
Real estate - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	8,185	9,334
Recorded Investment with No Allowance	7,362	6,777
Recorded Investment with Allowance	472	2,213
Total Recorded Investment	7,834	8,990
Related Allowance	245	733
Average Recorded Investment	8,412	9,925
Real estate - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	1,174	2,357
Recorded Investment with No Allowance	964	1,714
Recorded Investment with Allowance		223
Total Recorded Investment	964	1,937
Related Allowance		48
Average Recorded Investment	913	2,622
Real estate - Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance
Recorded Investment with No Allowance
Recorded Investment with Allowance
Total Recorded Investment
Related Allowance
Average Recorded Investment
Consumer - credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance
Recorded Investment with No Allowance
Recorded Investment with Allowance
Total Recorded Investment
Related Allowance
Average Recorded Investment
Consumer - other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	47	51
Recorded Investment with No Allowance	46	49
Recorded Investment with Allowance
Total Recorded Investment	46	49
Related Allowance
Average Recorded Investment	48	43
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance
Recorded Investment with No Allowance
Recorded Investment with Allowance
Total Recorded Investment
Related Allowance
Average Recorded Investment