Troubled Debt Restructurings by Class of Loan and Accrual Status (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	$ 286,626	$ 281,356
Residential
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	112,105	116,868
Land
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	9,707	9,972
Construction
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	11,896	6,979
Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	64,106	57,840
Commercial Business
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	19,192	20,776
Home Equity and Second Mortgage
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	37,644	38,887
Other Consumer
Financing Receivable, Modifications [Line Items]
Recorded investment in loans	31,976	30,034
Troubled Debt Restructuring
Financing Receivable, Modifications [Line Items]
Accruing	316	462
Nonaccrual	4,377	4,209
Recorded investment in loans	4,693	4,671
Related Allowance for Loan Losses	1,129	1,136
Troubled Debt Restructuring | Residential
Financing Receivable, Modifications [Line Items]
Accruing	181	112
Nonaccrual	690	516
Recorded investment in loans	871	628
Related Allowance for Loan Losses	102	11
Troubled Debt Restructuring | Land
Financing Receivable, Modifications [Line Items]
Accruing	135	135
Nonaccrual	0	0
Recorded investment in loans	135	135
Related Allowance for Loan Losses	0	0
Troubled Debt Restructuring | Construction
Financing Receivable, Modifications [Line Items]
Accruing	0	207
Nonaccrual	288	247
Recorded investment in loans	288	454
Related Allowance for Loan Losses	0	0
Troubled Debt Restructuring | Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Nonaccrual	1,557	1,603
Recorded investment in loans	1,557	1,603
Related Allowance for Loan Losses	87	211
Troubled Debt Restructuring | Commercial Business
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Nonaccrual	1,809	1,843
Recorded investment in loans	1,809	1,843
Related Allowance for Loan Losses	914	914
Troubled Debt Restructuring | Home Equity and Second Mortgage
Financing Receivable, Modifications [Line Items]
Accruing	0	8
Nonaccrual	33	0
Recorded investment in loans	33	8
Related Allowance for Loan Losses	26	0
Troubled Debt Restructuring | Other Consumer
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Nonaccrual	0	0
Recorded investment in loans	0	0
Related Allowance for Loan Losses	$ 0	$ 0