Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Dividend reinvestment plan, shares			17,683	22,278
Stock purchase and compensation plans, shares			484,491	537,588
Dividends to stockholders, per share	$ 0.18	$ 0.16	$ 0.54	$ 0.48
Acquisition of treasury stock, shares			108,311	136,012
Preferred stock, par value per share	$ 0	$ 0	$ 0	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	0	0	0	0
Series A Preferred Stock [Member]
Preferred stock, par value per share	$ 0	$ 0	$ 0	$ 0
Preferred stock, shares authorized	300,000	300,000	300,000	300,000

Aggregate dividends declared during the period for each share of common stock outstanding.

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