XML 26 R34.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Securities - Securities with unrealized losses aggregated by investment category and length of time (Detail) (USD $) | Sep. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | $ 71,901,000 | $ 33,555,000
Unrealized Loss, Less than 12 Months | (7,703,000) | (388,000)
Fair Value, 12 Months or More | 6,134,000 | 0
Unrealized Loss, 12 Months or More | (851,000) | 0
Fair Value | 78,035,000 | 33,555,000
Unrealized Loss | (8,554,000) | (388,000)
U.S. Government agency debt obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 70,142,000 | 33,555,000
Unrealized Loss, Less than 12 Months | (7,691,000) | (388,000)
Fair Value, 12 Months or More | 6,134,000 | 0
Unrealized Loss, 12 Months or More | (851,000) | 0
Fair Value | 76,276,000 | 33,555,000
Unrealized Loss | (8,542,000) | (388,000)
Mortgage-backed securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 0 | 0
Unrealized Loss, Less than 12 Months | 0 | 0
Fair Value, 12 Months or More | 0 | 0
Unrealized Loss, 12 Months or More | 0 | 0
Fair Value | 0 | 0
Unrealized Loss | 0 | 0
Michigan Strategic Fund bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 0 | 0
Unrealized Loss, Less than 12 Months | 0 | 0
Fair Value, 12 Months or More | 0 | 0
Unrealized Loss, 12 Months or More | 0 | 0
Fair Value | 0 | 0
Unrealized Loss | 0 | 0
Municipal general obligation bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 394,000 | 0
Unrealized Loss, Less than 12 Months | (1,000) | 0
Fair Value, 12 Months or More | 0 | 0
Unrealized Loss, 12 Months or More | 0 | 0
Fair Value | 394,000 | 0
Unrealized Loss | (1,000) | 0
Municipal revenue bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 0 | 0
Unrealized Loss, Less than 12 Months | 0 | 0
Fair Value, 12 Months or More | 0 | 0
Unrealized Loss, 12 Months or More | 0 | 0
Fair Value | 0 | 0
Unrealized Loss | 0 | 0
Mutual funds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value, Less than 12 Months | 1,365,000 | 0
Unrealized Loss, Less than 12 Months | (11,000) | 0
Fair Value, 12 Months or More | 0 | 0
Unrealized Loss, 12 Months or More | 0 | 0
Fair Value | 1,365,000 | 0
Unrealized Loss | $ (11,000) | $ 0

X
- Definition Available for sale securities continuous unrealized loss position aggregate losses accumulated in investments. + References No definition available. + Details
Name: | mbwm_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLossesAccumulatedInInvestments
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Available-for-sale securities continuous unrealized loss position less than twelve months aggregate losses accumulated in investments. + References No definition available. + Details
Name: | mbwm_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsAggregateLossesAccumulatedInInvestments
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Available for sale securities continuous unrealized loss position twelve months or longer aggregate losses accumulated in investments. + References No definition available. + Details
Name: | mbwm_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerAggregateLossesAccumulatedInInvestments
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration