Nonaccrual Loans and Loans Past Due Over Ninety Days Still on Accrual by Class (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	$ 18,506	[1]	$ 23,306	[1]	$ 28,317	[1]
Loans Past Due 90 Days or More and Still Accruing Interest	3,173
Real Estate Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	1,777		2,521		3,682
Loans Past Due 90 Days or More and Still Accruing Interest	531
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	334		373		323
Loans Past Due 90 Days or More and Still Accruing Interest	1,200
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	1,868		3,603		2,734
Residential Real Estate | Residential Real Estate - Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	9,298		12,183		13,356
Loans Past Due 90 Days or More and Still Accruing Interest	730
Residential Real Estate | Residential Real Estate - Non Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	1,376		1,565		1,880
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	3,756		3,032		6,265
Loans Past Due 90 Days or More and Still Accruing Interest	712
Consumer | Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loan	$ 97		$ 29		$ 77

[1] Loans on non-accrual status include impaired loans.