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 $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Impaired loans	$ 40,702	$ 48,773
Allowance	4,015	5,149
Unpaid principal balance in total impaired loans	50,019	73,333
Non Accrual Loans
Impaired loans	20,382	28,699
Restructuring | Accrual Loans
Impaired loans	10,839	10,110
Restructuring | Non Accrual Loans
Impaired loans	9,481	9,964
Commercial
Impaired loans	7,887	8,984
Allowance	1,940	2,597
Unpaid principal balance in total impaired loans	7,932	11,506
Commercial | Non Accrual Loans
Impaired loans	3,571	4,360
Commercial | Restructuring | Accrual Loans
Impaired loans	3,875	4,373
Commercial | Restructuring | Non Accrual Loans
Impaired loans	441	251
All Other
Impaired loans	6,541	6,430
Allowance	1,307	1,180
Unpaid principal balance in total impaired loans	2,821	6,904
All Other | Non Accrual Loans
Impaired loans	0	0
All Other | Restructuring | Accrual Loans
Impaired loans	4,215	4,234
All Other | Restructuring | Non Accrual Loans
Impaired loans	2,326	2,196
Impaired Financing Receivables with Related Allowance
Impaired loans	14,232	27,526
Impaired Financing Receivables with Related Allowance | Non Accrual Loans
Impaired loans	3,171	17,052
Impaired Financing Receivables with Related Allowance | Restructuring | Accrual Loans
Impaired loans	7,398	7,903
Impaired Financing Receivables with Related Allowance | Restructuring | Non Accrual Loans
Impaired loans	3,663	2,571
Impaired Financing Receivables with Related Allowance | Commercial
Impaired loans	4,974	5,723
Impaired Financing Receivables with Related Allowance | Commercial | Non Accrual Loans
Impaired loans	2,149	2,514
Impaired Financing Receivables with Related Allowance | Commercial | Restructuring | Accrual Loans
Impaired loans	2,693	2,981
Impaired Financing Receivables with Related Allowance | Commercial | Restructuring | Non Accrual Loans
Impaired loans	132	228
Impaired Financing Receivables with Related Allowance | All Other
Impaired loans	4,850	4,723
Impaired Financing Receivables with Related Allowance | All Other | Non Accrual Loans
Impaired loans	0	0
Impaired Financing Receivables with Related Allowance | All Other | Restructuring | Accrual Loans
Impaired loans	3,404	3,419
Impaired Financing Receivables with Related Allowance | All Other | Restructuring | Non Accrual Loans
Impaired loans	1,446	1,304
Impaired Financing Receivables with No Related Allowance
Impaired loans	26,470	21,247
Impaired Financing Receivables with No Related Allowance | Non Accrual Loans
Impaired loans	17,211	11,647
Impaired Financing Receivables with No Related Allowance | Restructuring | Accrual Loans
Impaired loans	3,441	2,207
Impaired Financing Receivables with No Related Allowance | Restructuring | Non Accrual Loans
Impaired loans	5,818	7,393
Impaired Financing Receivables with No Related Allowance | Commercial
Impaired loans	2,913	3,261
Impaired Financing Receivables with No Related Allowance | Commercial | Non Accrual Loans
Impaired loans	1,422	1,846
Impaired Financing Receivables with No Related Allowance | Commercial | Restructuring | Accrual Loans
Impaired loans	1,182	1,392
Impaired Financing Receivables with No Related Allowance | Commercial | Restructuring | Non Accrual Loans
Impaired loans	309	23
Impaired Financing Receivables with No Related Allowance | All Other
Impaired loans	1,691	1,707
Impaired Financing Receivables with No Related Allowance | All Other | Non Accrual Loans
Impaired loans	0	0
Impaired Financing Receivables with No Related Allowance | All Other | Restructuring | Accrual Loans
Impaired loans	811	815
Impaired Financing Receivables with No Related Allowance | All Other | Restructuring | Non Accrual Loans
Impaired loans	880	892
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Impaired loans	5,826	6,332
Allowance	149	0
Unpaid principal balance in total impaired loans	15,723	21,590
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Non Accrual Loans
Impaired loans	3,246	3,033
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	2,580	3,299
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Impaired loans	13,205	11,843
Allowance	242	774
Unpaid principal balance in total impaired loans	16,206	15,405
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	11,326	10,796
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Restructuring | Accrual Loans
Impaired loans	852	0
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	1,027	1,047
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Impaired loans	7,243	15,184
Allowance	377	598
Unpaid principal balance in total impaired loans	7,337	17,928
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	2,239	10,510
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Restructuring | Accrual Loans
Impaired loans	1,897	1,503
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Restructuring | Non Accrual Loans
Impaired loans	3,107	3,170
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Acquisition, Development and Construction
Impaired loans	1,055	0
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 | Accrual Loans
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	1,055	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate
Impaired loans	811	10,219
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	811	10,219
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Restructuring | Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate
Impaired loans	2,542	6,861
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	211	4,319
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Accrual Loans
Impaired loans	1,301	1,503
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Non Accrual Loans
Impaired loans	1,030	1,039
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction
Impaired loans	4,771	6,332
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Non Accrual Loans
Impaired loans	3,246	3,033
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Restructuring | Accrual Loans
Impaired loans	0	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Acquisition, Development and Construction | Restructuring | Non Accrual Loans
Impaired loans	1,525	3,299
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate
Impaired loans	12,394	1,624
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate | Non Accrual Loans
Impaired loans	10,515	577
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate | Restructuring | Accrual Loans
Impaired loans	852	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Investor Real Estate | Restructuring | Non Accrual Loans
Impaired loans	1,027	1,047
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate
Impaired loans	4,701	8,323
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Non Accrual Loans
Impaired loans	2,028	6,191
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Accrual Loans
Impaired loans	596	0
Commercial Real Estate Portfolio Segment | Impaired Financing Receivables with No Related Allowance | Commercial Owner Occupied Real Estate | Restructuring | Non Accrual Loans
Impaired loans	$ 2,077	$ 2,132