Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Property, buildings and equipment, accumulated depreciation	$ 38,927,654	$ 33,140,214
Finite-lived intangible assets, accumulated amortization	$ 263,134	$ 201,634
Preferred stock, par value (usd per share)	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value (usd per share)	$ 0.1	$ 0.1
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	27,813,772	27,813,772
Common stock, shares outstanding	25,451,354	25,451,354
Treasury stock, shares	2,362,418	2,362,418