Consolidated Statements of Changes in Stockholders' Equity Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends on perferred stock (in dollars per share)	$ 0	$ 150	$ 400
Dividends on common stock (in dollars per share)	$ 0.66	$ 0.62	$ 0.59
Issuance of common shares pursuant to the Dividend Reinvestment Plan (in shares)	30,059	50,446	59,717
Issuance of common shares pursuant to the Deferred Compensation Plan (in shares)	6,875	4,683	6,153
Issuance of common shares pursuant to the First Retirement & Savings Plan (in shares)	0	558	11,885
Issuance of restricted common shares pursuant to the Stock Incentive Plan (in shares)	47,339	2,910	3,281
Stock Issued During Period, Shares, Acquisitions	98,710	2,600,616
Stock Issued During Period, Shares, Conversion of Convertible Securities	0	1,355,319
number of preferred shares converted to common shares	0	5,500
Purchase of treasury shares (in shares)	20,734	0	53,246
Issuance of common shares pursuant to the exercise of stock options (in shares)	27,500	2,500	0
Common Stock
Stock issued during period, new issue (in shares)			1,392,859