Investment in Covered Impaired Loans, excluding Loans Accounted for under FASB ASC Topic 310-30 (Detail) (Covered Loans, Loans Excluded from FASB ASC Topic 310-30, Loans with no related allowance recorded, USD $) In Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 12,783	$ 12,783	$ 19,755
Unpaid Principal Balance	17,116	17,116	26,895
Related Allowance	0	0	0
Average Recorded Investment		14,763	18,086
Interest Income Recognized	54	163	398
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Investment	8,733	8,733	16,190
Unpaid Principal Balance	11,215	11,215	18,346
Related Allowance	0	0	0
Average Recorded Investment		11,262	12,324
Interest Income Recognized	51	144	316
Real estate-commercial
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,883	2,883	2,074
Unpaid Principal Balance	3,634	3,634	5,412
Related Allowance	0	0	0
Average Recorded Investment		2,183	3,910
Interest Income Recognized	0	2	14
Installment
Financing Receivable, Impaired [Line Items]
Recorded Investment			0
Unpaid Principal Balance			0
Related Allowance			0
Average Recorded Investment			255
Interest Income Recognized			0
Home equity
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,157	1,157	1,491
Unpaid Principal Balance	2,257	2,257	3,137
Related Allowance	0	0	0
Average Recorded Investment		1,311	1,597
Interest Income Recognized	3	17	68
All other
Financing Receivable, Impaired [Line Items]
Recorded Investment	10	10
Unpaid Principal Balance	10	10
Related Allowance	0	0
Average Recorded Investment		7
Interest Income Recognized	$ 0	$ 0