Consolidated Statements of Changes in Shareholders' Equity (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Stock [Member]
Common stock issued in connection with Firstbank merger (in shares)			8,087,272
Employee stock purchase plan, shares (in shares)	1,362	2,058	1,150
Dividend reinvestment plan, shares (in shares)	58,325	30,467	10,359
Stock option exercises, shares (in shares)	72,711	59,117	30,585
Stock grants to directors for retainer fees (in shares)	13,000	20,094	7,375
Cash dividends per common share (in dollars per share)			$ 2.48
Share repurchase program, shares (in shares)	167,878	788,541
Retained Earnings [Member]
Cash dividends per common share (in dollars per share)	$ 1.16	$ 0.58
Employee stock purchase plan, shares (in shares)	1,362	2,058