XML 57 R48.htm IDEA: XBRL DOCUMENT
v3.22.1

Note 3 - Loans and Allowance for Credit Losses - Loan Vintage (Details) - USD ($) | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Financing Receivable, Year One, Originated, Current Fiscal Year |  | $ 351,252,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 1,415,927,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 715,732,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 202,169,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 105,403,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 165,221,000 |
Financing Receivable, Term Loan |  | 2,955,704,000 |
Financing Receivable, Revolving |  | 600,086,000 |
Loans |  | 3,555,790,000 | $ 3,453,459,000
Commercial Portfolio Segment [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 282,130,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 1,175,663,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 612,694,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 183,912,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 87,423,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 111,668,000 |
Financing Receivable, Term Loan |  | 2,453,490,000 |
Financing Receivable, Revolving |  | 551,072,000 |
Loans |  | 3,004,562,000 | 2,950,424,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 55,010,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 368,442,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 133,448,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 25,677,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 7,900,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 12,794,000 |
Financing Receivable, Term Loan |  | 603,271,000 |
Financing Receivable, Revolving |  | 550,543,000 |
Loans | [1] | 1,153,814,000 | 1,137,419,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Grades 1-4 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 23,869,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 215,466,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 59,456,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 14,728,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 4,966,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 11,888,000 |
Financing Receivable, Term Loan |  | 330,373,000 |
Financing Receivable, Revolving |  | 388,894,000 |
Loans | [2] | 719,267,000 | 729,224,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Grades 5-7 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 27,468,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 148,260,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 73,905,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 10,949,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 2,874,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 850,000 |
Financing Receivable, Term Loan |  | 264,306,000 |
Financing Receivable, Revolving |  | 151,403,000 |
Loans |  | 415,709,000 | 398,378,000
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member] | Grades 8-9 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 3,673,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 4,716,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 87,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 60,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 56,000 |
Financing Receivable, Term Loan |  | 8,592,000 |
Financing Receivable, Revolving |  | 10,246,000 |
Loans |  | 18,838,000 | 9,817,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 11,668,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 34,432,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 4,537,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 116,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 17,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 1,394,000 |
Financing Receivable, Term Loan |  | 52,164,000 |
Financing Receivable, Revolving |  | 529,000 |
Loans |  | 52,693,000 | 43,239,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] | Grades 1-4 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 7,651,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 21,988,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 4,099,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 0 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 453,000 |
Financing Receivable, Term Loan |  | 34,191,000 |
Financing Receivable, Revolving |  | 355,000 |
Loans |  | 34,546,000 | 28,390,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] | Grades 5-7 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 4,017,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 12,444,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 438,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 116,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 0 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 842,000 |
Financing Receivable, Term Loan |  | 17,857,000 |
Financing Receivable, Revolving |  | 174,000 |
Loans |  | 18,031,000 | 14,730,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] | Grades 8-9 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 0 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 0 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 17,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 99,000 |
Financing Receivable, Term Loan |  | 116,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 116,000 | 119,000
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 102,148,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 273,868,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 111,263,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 36,614,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 35,503,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 23,336,000 |
Financing Receivable, Term Loan |  | 582,732,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 582,732,000 | 565,758,000
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member] | Grades 1-4 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 51,926,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 186,183,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 64,960,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 22,202,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 18,739,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 14,239,000 |
Financing Receivable, Term Loan |  | 358,249,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 358,249,000 | 346,082,000
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member] | Grades 5-7 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 50,222,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 87,685,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 46,255,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 12,241,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 16,595,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 9,097,000 |
Financing Receivable, Term Loan |  | 222,095,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 222,095,000 | 208,060,000
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member] | Grades 8-9 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 0 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 0 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 48,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 2,171,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 169,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 0 |
Financing Receivable, Term Loan |  | 2,388,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 2,388,000 | 11,616,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 75,576,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 406,430,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 309,530,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 111,608,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 37,124,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 67,093,000 |
Financing Receivable, Term Loan |  | 1,007,361,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 1,007,361,000 | 1,027,415,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member] | Grades 1-4 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 40,445,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 199,956,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 146,664,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 71,923,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 21,200,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 17,763,000 |
Financing Receivable, Term Loan |  | 497,951,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 497,951,000 | 503,482,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member] | Grades 5-7 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 35,131,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 193,821,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 162,866,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 39,685,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 15,924,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 49,330,000 |
Financing Receivable, Term Loan |  | 496,757,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 496,757,000 | 511,280,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member] | Grades 8-9 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 0 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 12,653,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 0 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 0 |
Financing Receivable, Term Loan |  | 12,653,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 12,653,000 | 12,653,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 37,728,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 92,491,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 53,916,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 9,897,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 6,879,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 7,051,000 |
Financing Receivable, Term Loan |  | 207,962,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 207,962,000 | 176,593,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member] | Grades 1-4 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 20,158,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 59,645,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 38,770,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 5,905,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 3,165,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 5,138,000 |
Financing Receivable, Term Loan |  | 132,781,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 132,781,000 | 119,473,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member] | Grades 5-7 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 17,570,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 32,757,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 15,146,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 3,992,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 3,714,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 1,855,000 |
Financing Receivable, Term Loan |  | 75,034,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 75,034,000 | 56,968,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member] | Grades 8-9 [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 0 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 89,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 0 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 0 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 58,000 |
Financing Receivable, Term Loan |  | 147,000 |
Financing Receivable, Revolving |  | 0 |
Loans |  | 147,000 | 152,000
Retail Portfolio Segment [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 69,122,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 240,264,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 103,038,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 18,257,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 17,980,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 53,553,000 |
Financing Receivable, Term Loan |  | 502,214,000 |
Financing Receivable, Revolving |  | 49,014,000 |
Loans |  | 551,228,000 | 503,035,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 67,861,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 235,895,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 101,123,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 16,365,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 17,173,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 52,618,000 |
Financing Receivable, Term Loan |  | 491,035,000 |
Financing Receivable, Revolving |  | 31,521,000 |
Loans |  | 522,556,000 | 442,547,000
Retail Portfolio Segment [Member] | Other Consumer Loans [Member] |  |  |
Financing Receivable, Year One, Originated, Current Fiscal Year |  | 1,261,000 |
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year |  | 4,369,000 |
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year |  | 1,915,000 |
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year |  | 1,892,000 |
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year |  | 807,000 |
Financing Receivable, Originated, More than Five Years before Current Fiscal Year |  | 935,000 |
Financing Receivable, Term Loan |  | 11,179,000 |
Financing Receivable, Revolving |  | 17,493,000 |
Loans | [3] | $ 28,672,000 | $ 60,488,000
[1] | For March 31, 2022, and December 31, 2021, includes $12.2 million and $40.1 million in loans originated under the Paycheck Protection Program, respectively.
[2] | Included in Commercial and Industrial Loans Grades 1 – 4 are $12.2 million of loans originated under the Paycheck Protection Program.
[3] | In conjunction with the adoption of the CECL methodology effective January 1, 2022, home equity lines of credit were reclassified to 1-4 family mortgage loans from other consumer loans. Home equity lines of credit totaled $31.9 million and $29.5 million as of March 31, 2022 and December 31, 2021, respectively.

X
- Definition Amortized cost of financing receivable term loan. + References No definition available. + Details
Name: | mbwm_FinancingReceivableTermLoan
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated more than five years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 + Details
Name: | us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated four years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 + Details
Name: | us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated in current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 + Details
Name: | us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated in fiscal year prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated three years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 + Details
Name: | us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated two years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 + Details
Name: | us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable that can be withdrawn, repaid, and redrawn. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableRevolving
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost, before allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(3)(b)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 14 -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 80 -URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922355-210448 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (1) Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (2) Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1404 -Paragraph (a) + Details
Name: | us-gaap_NotesReceivableGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_CommercialAndIndustrialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=mbwm_Grades1To4Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=mbwm_Grades5To7Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=mbwm_Grades8To9Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_RealEstateOwnerOccupiedLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_RealEstateNonOwnerOccupiedLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=mbwm_RetailPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_OneToFourFamilyMortgagesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_OtherConsumerLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |