Recorded Investment in Home Equity, Consumer and Residential Mortgage Loans Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,173,509	[1]	$ 1,129,305	[2]
Home Equity Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	74,068	[1]	77,323	[2]
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,782	[1]	47,595	[2]
Residential Mortgage Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	91,048	[1]	86,469	[2]
Performing [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	73,957		77,233
Performing [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,614		47,336
Performing [Member] | Residential Mortgage Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	90,626		85,721
Nonperforming [Member] | Home Equity Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	111		90
Nonperforming [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	168		259
Nonperforming [Member] | Residential Mortgage Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 422		$ 748

[1] Total recorded investment in loans includes $5,363 in accrued interest.

[2] Total recorded investment in loans includes $5,756 in accrued interest.