Summary of Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Impaired loans with a valuation allowance	$ 15,833	$ 36,742
Impaired loans without a valuation allowance	34,570	30,833
Total impaired loans	50,403	67,575
Allowance for loan and lease losses related to impaired loans	3,746	7,791
Allowance for loan and lease losses related to loans collectively evaluated	38,872	41,635
Total allowance for loan and lease losses	42,618	49,426
Average impaired loans for the period	59,353	68,377
Contractual interest income due on impaired loans during the period	3,168	4,973
Interest income on impaired loans recognized on a cash basis	927	1,523
Interest income on impaired loans recognized on an accrual basis	$ 403	$ 325

Loans and Leases Receivable, Impaired, Contractual Interest Income

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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