XML 38 R50.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Securities - Amortized Cost and Fair Value of Available for Sale Securities and Related Pre-tax Gross Unrealized Gains and Losses (Detail) (USD $) | Dec. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 139,487,000 | $ 134,664,000
Gross Unrealized Gains | 1,791,000 | 4,038,000
Gross Unrealized Losses | (10,100,000) | (388,000)
Fair Value | 131,178,000 | 138,314,000
U.S. Government agency debt obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 108,279,000 | 78,447,000
Gross Unrealized Gains | 263,000 | 1,039,000
Gross Unrealized Losses | (10,065,000) | (388,000)
Fair Value | 98,477,000 | 79,098,000
Mortgage-backed securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 12,456,000 | 20,182,000
Gross Unrealized Gains | 1,102,000 | 1,814,000
Gross Unrealized Losses | 0 | 0
Fair Value | 13,558,000 | 21,996,000
Michigan Strategic Fund bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 0 | 11,255,000
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Fair Value | 0 | 11,255,000
Municipal general obligation bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 16,488,000 | 21,700,000
Gross Unrealized Gains | 388,000 | 1,043,000
Gross Unrealized Losses | (4,000) | 0
Fair Value | 16,872,000 | 22,743,000
Municipal revenue bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 878,000 | 1,726,000
Gross Unrealized Gains | 38,000 | 91,000
Gross Unrealized Losses | 0 | 0
Fair Value | 916,000 | 1,817,000
Mutual funds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 1,386,000 | 1,354,000
Gross Unrealized Gains | 0 | 51,000
Gross Unrealized Losses | (31,000) | 0
Fair Value | $ 1,355,000 | $ 1,405,000

X
- Definition Available for sale securities gross unrealized gains accumulated in investments. + References No definition available. + Details
Name: | mbwm_AvailableForSaleSecuritiesGrossUnrealizedGainsAccumulatedInInvestments
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_AvailableForSaleSecuritiesAmortizedCost
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