Average Recorded Investment and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 201,898	$ 169,204	$ 194,726	$ 161,668
Interest Income Recognized	1,664	2,165	3,870	4,904
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	130,481	113,379	121,821	105,403
Interest Income Recognized	1,090	1,584	2,167	3,202
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,908	28	829	28
Interest Income Recognized	2		9	1
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	43,184	37,648	49,272	37,986
Interest Income Recognized	347	393	1,095	1,132
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	108,561	81,638	99,939	71,968
Interest Income Recognized	993	739	1,984	2,095
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	21,920	31,741	21,882	33,435
Interest Income Recognized	97	845	183	1,107
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	26,325	18,149	22,804	18,251
Interest Income Recognized	225	188	599	569
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,908	28	829	28
Interest Income Recognized	$ 2		$ 9	$ 1