Subordinated Debentures (Details) (USD $)	1 Months Ended			1 Months Ended
	Sep. 30, 2004	Sep. 16, 2004 Series A Notes [Member] Mercantile Bank Capital Trust [Member]	Dec. 10, 2004 Series B Notes [Member] Mercantile Bank Capital Trust [Member]	Sep. 16, 2004 Series A Preferred Stock [Member]	Dec. 10, 2004 Series B Preferred Stock [Member]	Sep. 30, 2004 Common Class A [Member] Mercantile Bank Capital Trust [Member]	Dec. 31, 2004 Common Class B [Member] Mercantile Bank Capital Trust [Member]
Subordinated Borrowing [Line Items]
Series A and B Preferred Securities sold in a private sale				$ 16,000,000	$ 16,000,000
Series A and B Common Securities sold by trust to Mercantile						495,000	495,000
Proceeds of series A preferred securities and series A common securities used to purchase of series A floating rate notes		16,495,000	16,495,000
Subordinated Debentures (Textual) [Abstract]
Preferred Securities percentage	9.60%
Proceeds of Series A floating rate notes to finance redemption	$ 16,000,000