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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2013 Segment | Dec. 31, 2012
Schedule Of Significant Accounting Policies [Line Items] |  |
Mercantile Bank Corporation incorporation date | Jul. 15, 1997 |
Mercantile Bank Corporation operational date | Dec. 15, 1997 |
Date Mercantile Bank Mortgage Company was reorganized as Mercantile Bank Mortgage Company, LLC | Jan. 01, 2004 |
Percentage of ownership by the Bank for limited liability company | 99.00% |
Percentage of ownership interest distributed to insurance company | 1.00% |
Mortgage company's dissolution date | Jan. 01, 2013 |
Maturities of short-term borrowings reported net for cash flow purposes | 90 days or less |
Net unamortized deferred loan fees amounted | $ 0.5 | $ 0.7
Delinquent period on commercial and mortgage Loans | 90 days |
Maximum period of Consumer and credit card loans | 120 days |
Loans held for sale | $ 1.1 | $ 3.5
Reversed the full valuation allowance against the net deferred tax asset that was initially recorded at December 31, 2009 | Dec. 31, 2011 |
Number of operating Segments | 1 |
Buildings and related components [Member] | Minimum [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Property and Equipment Useful lives | 5 years |
Buildings and related components [Member] | Maximum [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Property and Equipment Useful lives | 33 years |
Furniture and Fixtures [Member] | Minimum [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Property and Equipment Useful lives | 3 years |
Furniture and Fixtures [Member] | Maximum [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Property and Equipment Useful lives | 7 years |
Mercantile Bank Mortgage Company [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Bank subsidiary year of formation | 2000 |
Mercantile Bank Mortgage Company initiated business and Real Estate | Oct. 24, 2000 |
Mercantile Insurance Company [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Bank subsidiary year of formation | 2002 |
Ownership percentage of Mercantile Bank Mortgage Company, LLC | 1.00% |
Mercantile Real Estate [Member] |  |
Schedule Of Significant Accounting Policies [Line Items] |  |
Mercantile Bank Mortgage Company initiated business and Real Estate | Jul. 21, 2003 |
Date of facility operations | Jun. 30, 2005 |

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