Stock Option Plan (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock Options Issued

	Directors									Officers
Grant date	May 11, 2018			May 3, 2019			April 24, 2020			May 11, 2018			May 3, 2019			April 24, 2020
Exercise price	$	49.46		$	55.71		$	50.00		$	49.46		$	55.71		$	50.00
Volatility	0.192			0.236			0.258			0.177			0.206			0.240
Expected life (years)	5.0			5.0			5.0			7.0			7.0			7.0
Assumed yield	3.70		%	3.75		%	3.80		%	3.75		%	3.80		%	3.85		%
Risk-free rate	2.84		%	2.33		%	0.36		%	2.94		%	2.43		%	0.51		%

Summary of Option Activity

The table below summarizes the option activity for the years 2020, 2019, and 2018:

	2020			2019			2018
	Shares	Weighted Average Exercise Price		Shares	Weighted Average Exercise Price		Shares	Weighted Average Exercise Price
Outstanding at January 1	1,309,614	$	53.38	1,114,169	$	52.40	913,320	$	52.80
Granted	238,000	50.00		260,000	55.71		245,000	49.46
Exercised	(10,749)	49.19		(57,055)	44.53		(39,151)	42.98
Expired/Forfeited	(34,195)	54.09		(7,500)	56.07		(5,000)	54.78
Outstanding December 31	1,502,670	52.86		1,309,614	53.38		1,114,169	52.40
Exercisable at December 31	971,545	53.01		763,614	52.43		600,919	50.93