Recorded Investment with Respect to Impaired loans, Associated Allowance by Applicable Portfolio Segment and Principal Balance of Impaired Loans prior to Amounts Charged-off (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Impaired loans	$ 48,773,000	$ 67,575,000	$ 69,614,000
Allowance	5,149,000	7,791,000
Unpaid principal balance in total impaired loans	73,333,000	82,600,000
Non Accrual Loans
Impaired loans	28,699,000	40,467,000
Restructuring | Accrual Loans
Impaired loans	10,110,000	6,881,000
Restructuring | Non Accrual Loans
Impaired loans	9,964,000	20,227,000
Commercial Loan
Impaired loans	8,984,000	9,092,000
Allowance	2,597,000	1,037,000
Unpaid principal balance in total impaired loans	11,506,000	11,303,000
Commercial Loan | Non Accrual Loans
Impaired loans	4,360,000	4,526,000
Commercial Loan | Restructuring | Accrual Loans
Impaired loans	4,373,000	1,866,000
Commercial Loan | Restructuring | Non Accrual Loans
Impaired loans	251,000	2,700,000
All Other
Impaired loans	6,430,000	7,402,000
Allowance	1,180,000	1,595,000
Unpaid principal balance in total impaired loans	6,904,000	0
All Other | Non Accrual Loans
Impaired loans	0	1,893,000
All Other | Restructuring | Accrual Loans
Impaired loans	4,234,000	4,308,000
All Other | Restructuring | Non Accrual Loans
Impaired loans	2,196,000	1,201,000
Impaired Financing Receivables with Related Allowance
Impaired loans	27,526,000	36,742,000
Impaired Financing Receivables with Related Allowance | Non Accrual Loans
Impaired loans	11,647,000	20,106,000
Impaired Financing Receivables with Related Allowance | Restructuring | Accrual Loans
Impaired loans	7,903,000	5,528,000
Impaired Financing Receivables with Related Allowance | Restructuring | Non Accrual Loans
Impaired loans	2,571,000	11,108,000
Impaired Financing Receivables with Related Allowance | Commercial Loan
Impaired loans	5,723,000	2,763,000
Impaired Financing Receivables with Related Allowance | Commercial Loan | Non Accrual Loans
Impaired loans	2,514,000	1,110,000
Impaired Financing Receivables with Related Allowance | Commercial Loan | Restructuring | Accrual Loans
Impaired loans	2,981,000	1,346,000
Impaired Financing Receivables with Related Allowance | Commercial Loan | Restructuring | Non Accrual Loans
Impaired loans	228,000	307,000
Impaired Financing Receivables with Related Allowance | All Other
Impaired loans	4,723,000	4,955,000
Impaired Financing Receivables with Related Allowance | All Other | Non Accrual Loans
Impaired loans	0	1,093,000
Impaired Financing Receivables with Related Allowance | All Other | Restructuring | Accrual Loans
Impaired loans	3,419,000	3,475,000
Impaired Financing Receivables with Related Allowance | All Other | Restructuring | Non Accrual Loans
Impaired loans	892,000	387,000
Impaired Financing Receivables with No Related Allowance
Impaired loans	21,247,000	30,833,000
Impaired Financing Receivables with No Related Allowance | Non Accrual Loans
Impaired loans	17,052,000	20,361,000
Impaired Financing Receivables with No Related Allowance | Restructuring | Accrual Loans
Impaired loans	2,207,000	1,353,000
Impaired Financing Receivables with No Related Allowance | Restructuring | Non Accrual Loans
Impaired loans	7,393,000	9,119,000
Impaired Financing Receivables with No Related Allowance | Commercial Loan
Impaired loans	3,261,000	6,329,000
Impaired Financing Receivables with No Related Allowance | Commercial Loan | Non Accrual Loans
Impaired loans	1,846,000	3,416,000
Impaired Financing Receivables with No Related Allowance | Commercial Loan | Restructuring | Accrual Loans
Impaired loans	1,392,000	520,000
Impaired Financing Receivables with No Related Allowance | Commercial Loan | Restructuring | Non Accrual Loans
Impaired loans	23,000	2,393,000
Impaired Financing Receivables with No Related Allowance | All Other
Impaired loans	1,707,000	2,447,000
Impaired Financing Receivables with No Related Allowance | All Other | Non Accrual Loans
Impaired loans	0	800,000
Impaired Financing Receivables with No Related Allowance | All Other | Restructuring | Accrual Loans
Impaired loans	815,000	833,000
Impaired Financing Receivables with No Related Allowance | All Other | Restructuring | Non Accrual Loans
Impaired loans	1,304,000	814,000
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Impaired loans	6,332,000	18,701,000
Allowance	0	7,000
Unpaid principal balance in total impaired loans	21,590,000	37,442,000
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Non Accrual Loans
Impaired loans	3,033,000	7,798,000
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Restructuring | Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Restructuring | Non Accrual Loans
Impaired loans	3,170,000	10,903,000
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Impaired loans	11,843,000	16,964,000
Allowance	774,000	3,380,000
Unpaid principal balance in total impaired loans	15,405,000	17,389,000
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	10,796,000	15,695,000
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Restructuring | Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	1,047,000	1,269,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Impaired loans	15,184,000	15,416,000
Allowance	598,000	1,772,000
Unpaid principal balance in total impaired loans	17,928,000	16,466,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	10,510,000	10,555,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Restructuring | Accrual Loans
Impaired loans	1,503,000	707,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Restructuring | Non Accrual Loans
Impaired loans	3,170,000	4,154,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Acquisition, Development and Construction
Impaired loans	0	6,504,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Acquisition, Development and Construction | Non Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Acquisition, Development and Construction | Restructuring
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Acquisition, Development and Construction | Restructuring | Non Accrual Loans
Impaired loans	0	6,504,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate
Impaired loans	10,219,000	14,440,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	10,219,000	13,812,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Restructuring
Impaired loans	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	0	628,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate
Impaired loans	6,861,000	8,080,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	4,319,000	4,091,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Accrual Loans
Impaired loans	1,503,000	707,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction
Impaired loans	8,323,000	12,197,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Non Accrual Loans
Impaired loans	3,033,000	7,798,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Restructuring | Non Accrual Loans
Impaired loans	3,299,000	4,399,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate
Impaired loans	1,624,000	2,524,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	577,000	1,883,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	1,047,000	641,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate
Impaired loans	8,323,000	7,336,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	6,191,000	6,464,000
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Restructuring
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Non Accrual Loans
Impaired loans	$ 2,132,000	$ 872,000