Consolidated Balance Sheets (Parenthetical) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Property, buildings and equipment, accumulated depreciation	$ 54,491,653	$ 51,904,568
Finite-lived intangible assets, accumulated amortization	$ 399,843	$ 384,801
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)	$ 0.10	$ 0.10
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	27,813,772	27,813,772
Common stock, shares outstanding	24,522,534	24,522,534
Treasury stock, shares	3,291,238	3,291,238