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Loans and Allowance for Loan Losses (Details 10) (USD $) | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011
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Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | $ 24,947,000 | $ 26,035,000 | $ 28,677,000 | $ 29,689,000 | $ 30,943,000 | $ 36,532,000
Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 13,714,000 |  | 13,097,000 |  |  |
Commercial and industrial [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 680,000 |  | 772,000 |  |  |
Vacant land, land development and residential construction [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 1,204,000 |  | 713,000 |  |  |
Real estate - owner occupied [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 921,000 |  | 1,116,000 |  |  |
Real estate - non-owner occupied [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 9,517,000 |  | 9,751,000 |  |  |
Real estate - multi-family and residential rental [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 748,000 |  | 745,000 |  |  |
Total commercial [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 13,070,000 |  | 13,097,000 |  |  |
Home equity and other [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 0 |  | 0 |  |  |
1 - 4 family mortgages [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | 644,000 |  | 0 |  |  |
Total retail [Member] | Financing Receivable Modified as Troubled Debt [Member] |  |  |  |  |  |
Allowance related to loans categorized as troubled debt restructurings |  |  |  |  |  |
Total | $ 644,000 |  | $ 0 |  |  |

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- Details
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Namespace Prefix: | mbwm_
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- Definition A valuation allowance for financing receivables that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524 + Details
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