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Note 21 - Regulatory Matters (Details) - Actual Capital Levels and Minimum Levels (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Consolidated Entities [Member] |  |
Total capital (to risk weighted assets) |  |
Total capital (to risk weighted assets), actual amount | $ 334,793 us-gaap_Capital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | $ 193,925 us-gaap_Capital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Total capital (to risk weighted assets), actual ratio | 14.40%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 15.90%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Total capital (to risk weighted assets), minimum required for capital adequacy purposes amount | 185,553 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 97,498 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Total capital (to risk weighted assets), minimum required for capital adequacy purposes ratio | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Total capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations amount |  |
Total capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations ratio |  |
Tier 1 capital (to risk weighted assets) |  |
Tier 1 capital (to risk weighted assets), actual amount | 314,752 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 178,598 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk weighted assets), actual ratio | 13.60%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 14.70%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk weighted assets), minimum required for capital adequacy purposes amount | 92,777 us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 48,749 us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk weighted assets), minimum required for capital adequacy purposes ratio | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations amount |  |
Tier 1 capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations ratio |  |
Tier 1 capital (to average assets) |  |
Tier 1 capital (to average assets), actual amount | 314,752 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 178,598 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to average assets), actual ratio | 11.20%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 12.50%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to average assets), minimum required for capital adequacy purposes amount | 112,949 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 57,006 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk average assets), minimum required for capital adequacy purposes ratio | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember
Tier 1 capital (to risk average assets), minimum required to be well capitalized under prompt corrective action regulations amount |  |
Tier 1 capital (to risk average assets), minimum required to be well capitalized under prompt corrective action regulations ratio |  |
Bank [Member] |  |
Total capital (to risk weighted assets) |  |
Total capital (to risk weighted assets), actual amount | 332,749 us-gaap_Capital / dei_LegalEntityAxis = mbwm_BankMember | 190,493 us-gaap_Capital / dei_LegalEntityAxis = mbwm_BankMember
Total capital (to risk weighted assets), actual ratio | 14.40%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 15.70%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Total capital (to risk weighted assets), minimum required for capital adequacy purposes amount | 185,309 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember | 97,329 us-gaap_CapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember
Total capital (to risk weighted assets), minimum required for capital adequacy purposes ratio | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 8.00%us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Total capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations amount | 231,636 us-gaap_CapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember | 121,662 us-gaap_CapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember
Total capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations ratio | 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 10.00%us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets) |  |
Tier 1 capital (to risk weighted assets), actual amount | 312,708 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = mbwm_BankMember | 175,192 us-gaap_TierOneRiskBasedCapital / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets), actual ratio | 13.50%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 14.40%us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets), minimum required for capital adequacy purposes amount | 92,655 us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember | 48,665 us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets), minimum required for capital adequacy purposes ratio | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 4.00%us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations amount | 138,982 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember | 72,997 us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk weighted assets), minimum required to be well capitalized under prompt corrective action regulations ratio | 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember | 6.00%us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to average assets) |  |
Tier 1 capital (to average assets), actual amount | 312,708 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = mbwm_BankMember | 175,192 us-gaap_TierOneLeverageCapital / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to average assets), actual ratio | 11.10%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember | 12.30%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to average assets), minimum required for capital adequacy purposes amount | 112,856 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember | 56,860 us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk average assets), minimum required for capital adequacy purposes ratio | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember | 4.00%us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk average assets), minimum required to be well capitalized under prompt corrective action regulations amount | $ 141,070 us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember | $ 71,075 us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized / dei_LegalEntityAxis = mbwm_BankMember
Tier 1 capital (to risk average assets), minimum required to be well capitalized under prompt corrective action regulations ratio | 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember | 5.00%us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets / dei_LegalEntityAxis = mbwm_BankMember

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- Definition The amount of total capital as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998 + Details
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- Definition The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Total Capital divided by risk weighted assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 Risk Based Capital as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
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- Definition The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 capital divided by risk weighted assets as defined by regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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