CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 1.82	$ 1.77	$ 1.70
Net exercise of stock options and related tax benefit (in shares)	22,277	39,931	80,681
Common stock repurchased and returned to unissued status (in shares)		22,356	67,481
Shares issued for dividend reinvestment plan (in shares)	34,750	45,148
Shares issued for employee stock ownership plan (in shares)	27,412	31,435	29,575
Directors deferred compensation plan (in shares)	2,808	1,871	4,690
Restricted stock activity (in shares)	45,269	29,511	40,505
Shares issued for purchase acquisition (in shares)		32,553	960