Note 24 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements - Condensed Statement of Cash Flows (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 31,913,000	$ 27,020,000	$ 17,331,000
Adjustments to reconcile net income to net cash from operating activities:
Stock-based compensation expense	1,459,000	684,000	714,000
Stock grants to directors for retainer fees	327,000	403,000	155,000
Gain on trust preferred securities repurchase	(2,970,000)	0	0
Other assets	(648,000)	(4,815,000)	1,795,000
Change in other liabilities	(1,046,000)	4,185,000	(9,822,000)
Net cash from operating activities	34,602,000	36,004,000	14,439,000
Cash flows from investing activities
Proceeds from stock option exercises, net of cashless exercises	978,000	891,000	282,000
Employee stock purchase plan	36,000	44,000	23,000
Dividend reinvestment plan	1,601,000	655,000	209,000
Repurchase of common stock	(3,732,000)	(15,762,000)	0
Payment of cash dividends to common shareholders	(18,731,000)	(9,516,000)	(24,464,000)
Repurchase of trust preferred securities	(8,030,000)	0	0
Net change in cash and cash equivalents	93,705,000	(82,847,000)	25,773,000
Parent Company [Member]
Cash flows from operating activities
Net income	31,913,000	27,020,000	17,331,000
Adjustments to reconcile net income to net cash from operating activities:
Equity in undistributed net income of subsidiary	(3,999,000)	(5,648,000)	(9,131,000)
Stock-based compensation expense	1,459,000	684,000	714,000
Stock grants to directors for retainer fees	327,000	403,000	155,000
Gain on trust preferred securities repurchase	(2,970,000)	0	0
Other assets	387,000	11,000	(8,163,000)
Change in other liabilities	78,000	4,717,000	21,979,000
Net cash from operating activities	27,195,000	27,187,000	22,885,000
Cash flows from investing activities
Proceeds from stock option exercises, net of cashless exercises	978,000	891,000	282,000
Employee stock purchase plan	36,000	44,000	23,000
Dividend reinvestment plan	1,601,000	655,000	209,000
Repurchase of common stock	(3,732,000)	(15,762,000)	0
Payment of cash dividends to common shareholders	(18,731,000)	(9,516,000)	(24,464,000)
Repurchase of trust preferred securities	(8,030,000)	0	0
Net cash for financing activities	(27,878,000)	(23,688,000)	(23,950,000)
Net change in cash and cash equivalents	(683,000)	3,499,000	(1,065,000)
Cash and cash equivalents at beginning of period	4,940,000	1,441,000	2,506,000
Cash and cash equivalents at end of period	$ 4,257,000	$ 4,940,000	$ 1,441,000