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Note 1 - Significant Accounting Policies (Details Textual) |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 14, 2021 USD ($) | Apr. 30, 2020 | Sep. 30, 2021 USD ($) shares | Sep. 30, 2020 USD ($) shares | Sep. 30, 2021 USD ($) shares | Sep. 30, 2020 USD ($) shares | May 31, 2021 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Aug. 08, 2020 USD ($) | Jul. 15, 2020 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities |  |  | 5 |  | 5 |  |  |  |  |  |
Interest Income on Commercial and Mortgage Loans Discontinued Period (Day) |  |  |  |  | 90 days |  |  |  |  |  |
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off (Day) |  |  |  |  | 120 days |  |  |  |  |  |
Mortgages Held-for-sale, Fair Value Disclosure |  |  | $ 49,100,000 |  | $ 49,100,000 |  |  |  | $ 24,000,000.0 |  |
Servicing Asset, Total |  |  | 1,260,000,000 |  | 1,260,000,000 |  |  |  | 1,040,000,000.00 |  |
Property, Plant and Equipment, Net, Ending Balance |  |  | $ 57,465,000 |  | $ 57,465,000 |  |  |  | 58,959,000 |  |
Revision of Prior Period, Adjustment [Member] |  |  |  |  |  |  |  |  |  |  |
Property, Plant and Equipment, Net, Ending Balance |  |  |  |  |  |  |  | $ 2,700,000 | 2,800,000 |  |
Other Liabilities, Total |  |  |  |  |  |  |  | $ 2,700,000 | $ 2,800,000 |  |
Hastings, Michigan Branch Office [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] |  |  |  |  |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net | $ 9,700,000 |  |  |  |  |  |  |  |  |  |
Proceeds from Sale of Property Held-for-sale | 1,500,000 |  |  |  |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Liabilities, Total | $ 14,600,000 |  |  |  |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Deposit Accounts, Premium of Book Balance | 5.00% |  |  |  |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Deposit Premium | $ 700,000 |  |  |  |  |  |  |  |  |  |
Hastings, Michigan Branch Office [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Branch Facility [Member] |  |  |  |  |  |  |  |  |  |  |
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal | $ 300,000 |  |  |  |  |  |  |  |  |  |
Core Deposits [Member] |  |  |  |  |  |  |  |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (Year) |  |  |  |  | 10 years |  |  |  |  |  |
Restricted Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights (in shares) | shares |  |  | 260,000 | 255,000 | 260,000 | 255,000 |  |  |  |  |
Share-based Payment Arrangement, Option [Member] |  |  |  |  |  |  |  |  |  |  |
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights (in shares) | shares |  |  | 3,000 | 2,000 | 3,000 | 2,000 |  |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) | shares |  |  | 7,000 | 9,000 | 7,000 | 9,000 |  |  |  |  |
Commercial Portfolio Segment [Member] |  |  |  |  |  |  |  |  |  |  |
Financing Receivable, Payment Deferrals, Interest-only Amendments, Period (Day) |  | 90 days |  |  |  |  |  |  |  |  |
Financing Receivable, Payment Deferrals, Principal and Interest, Period (Day) |  | 90 days |  |  |  |  |  |  |  |  |
Financing Receivable, Payment Deferrals, Interest Rate |  | 0.00% |  |  |  |  |  |  |  |  |
Financing Receivable, Number of Principal and Interest Payment Deferrals |  |  | 0 |  | 0 |  |  |  |  |  | 750
Financing Receivable, Principal and Interest Deferred Payments |  |  |  |  |  |  |  |  |  |  | $ 719,000,000
Retail Portfolio Segment [Member] |  |  |  |  |  |  |  |  |  |  |
Financing Receivable, Payment Deferrals, Principal and Interest, Period (Day) |  | 90 days |  |  |  |  |  |  |  |  |
Financing Receivable, Number of Principal and Interest Payment Deferrals |  |  | 6 | 260 | 6 | 260 |  |  |  |  |
Financing Receivable, Principal and Interest Deferred Payments |  |  | $ 500,000 | $ 23,800,000 | $ 500,000 | $ 23,800,000 |  |  |  |  |
SBA, CARES Act, Paycheck Protection Program [Member] |  |  |  |  |  |  |  |  |  |  |
Number of Loans Originated Under the Paycheck Protection Program |  |  |  |  |  |  |  |  |  | 2,200 |
Financing Receivable, before Allowance for Credit Loss, Total |  |  |  |  |  |  |  |  |  | $ 553,000,000 |
Financing Receivable, Forgiveness Transactions, Number of Loans |  |  | 2,100 |  | 2,100 |  |  |  |  |  |
Financing Receivable, Forgiveness Transactions |  |  | $ 550,000,000 |  | $ 550,000,000 |  |  |  |  |  |
Amortization of Deferred Loan Origination Fees, Net |  |  |  |  | $ 3,700,000 |  |  |  |  |  |
SBA, CARES Act, Paycheck Protection Program, Round Two [Member] |  |  |  |  |  |  |  |  |  |  |
Number of Loans Originated Under the Paycheck Protection Program |  |  |  |  |  |  | 1,200 |  |  |  |
Financing Receivable, before Allowance for Credit Loss, Total |  |  |  |  |  |  | $ 209,000,000 |  |  |  |
Financing Receivable, Forgiveness Transactions, Number of Loans |  |  | 600 |  | 600 |  |  |  |  |  |
Financing Receivable, Forgiveness Transactions |  |  | $ 95,900,000 |  | $ 95,900,000 |  |  |  |  |  |
Amortization of Deferred Loan Origination Fees, Net |  |  |  |  | $ 4,800,000 |  |  |  |  |  |

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