Allowance For Loan Losses and Credit Quality Information (Narrative) (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Contract	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Interest income on impaired loans	$ 150,000	$ 478,000
Book balance of troubled debt restructuring	22,300,000	22,300,000	27,700,000
TDRs in nonaccrual status		12,100,000	18,800,000
TDRs in accrual status		10,200,000	8,900,000
Troubled debt restructuring specific reserves	1,200,000	1,200,000	1,300,000
Number of notes modified in troubled debt restructurings		104
Increased in allowance for loan losses		357,000
TDR Charge-offs	8,100,000	8,100,000
Residential TDR	$ 84,000	$ 84,000
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of notes modified in troubled debt restructurings		15