Note 22 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements - Condensed Balance Sheets (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
ASSETS
Other assets	$ 94,993,000	$ 54,267,000
Total assets	4,872,619,000	5,257,749,000
LIABILITIES AND SHAREHOLDERS' EQUITY
Liabilities	4,431,211,000	4,801,190,000
Subordinated debentures	48,958,000	48,244,000
Subordinated notes	88,628,000	73,646,000
Shareholders’ equity	441,408,000	456,559,000	$ 441,554,000	$ 416,561,000
Total liabilities and shareholders’ equity	4,872,619,000	5,257,749,000
Parent Company [Member]
ASSETS
Cash and cash equivalents	18,633,000	14,570,000
Investment in bank subsidiary	543,599,000	545,691,000
Other assets	19,786,000	19,576,000
Total assets	582,018,000	579,837,000
LIABILITIES AND SHAREHOLDERS' EQUITY
Liabilities	3,024,000	1,388,000
Subordinated debentures	48,958,000	48,244,000
Subordinated notes	88,628,000	73,646,000
Shareholders’ equity	441,408,000	456,559,000
Total liabilities and shareholders’ equity	$ 582,018,000	$ 579,837,000