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Note 3 - Loans and Allowance for Loan Losses - Activity for Troubled Debt Restructurings (Details) - USD ($) | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] |  |
Beginning Balance | $ 6,414,000 | $ 8,587,000
Charge-Offs | 0 | 0
Payments | (2,676,000) | (2,832,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 22,000 | 6,449,000
Ending Balance | 3,760,000 | 12,204,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] |  |
Beginning Balance | 0 | 85,000
Charge-Offs | 0 | 0
Payments | 0 | (3,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 0 | 0
Ending Balance | 0 | 82,000
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member] |  |
Beginning Balance | 14,797,000 | 1,145,000
Charge-Offs | 0 | 0
Payments | (910,000) | (988,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 0 | 3,654,000
Ending Balance | 13,887,000 | 3,811,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member] |  |
Beginning Balance | 480,000 | 178,000
Charge-Offs | 0 | 0
Payments | (9,000) | (4,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 0 | 0
Ending Balance | 471,000 | 174,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member] |  |
Beginning Balance | 0 | 7,000
Charge-Offs | 0 | 0
Payments | 0 | (4,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 0 | 0
Ending Balance | 0 | 3,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] |  |
Beginning Balance | 1,146,000 | 1,415,000
Charge-Offs | 0 | 0
Payments | (118,000) | (29,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 71,000 | 66,000
Ending Balance | 1,099,000 | 1,452,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] |  |
Beginning Balance | 806,000 | 724,000
Charge-Offs | 0 | 0
Payments | (22,000) | (9,000)
Transfers to ORE | 0 | 0
Net Additions/Deletions | 36,000 | 0
Ending Balance | $ 820,000 | $ 715,000

X
- Definition A financing receivable which had its terms modified during the period and is now considered a troubled restructuring. + References No definition available. + Details
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Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reflects the amount of the charge-off related to a troubled debt restructuring. + References No definition available. + Details
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- Definition The cash inflow associated with a financing receivable classified as a troubled debt restructuring. + References No definition available. + Details
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- Definition Amount of financing receivable modified as troubled debt restructuring. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554 + Details
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