Stock Option Plan (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Stock Options Issued

	Directors									Officers
Grant date	May 5, 2017			May 11, 2018			May 3, 2019			May 5, 2017			May 11, 2018			May 3, 2019
Exercise price	$	59.41		$	49.46		$	55.71		$	59.41		$	49.46		$	55.71
Volatility	0.173			0.192			0.236			0.170			0.177			0.206
Expected life (years)	5.0			5.0			5.0			7.0			7.0			7.0
Assumed yield	3.45		%	3.70		%	3.75		%	3.50		%	3.75		%	3.80		%
Risk-free rate	1.89		%	2.84		%	2.33		%	2.17		%	2.94		%	2.43		%

Summary of Option Activity

The table below summarizes the option activity for the years 2019, 2018, and 2017:

	2019				2018				2017
	Shares		Weighted Average Exercise Price		Shares		Weighted Average Exercise Price		Shares		Weighted Average Exercise Price
Outstanding at January 1	1,114,169		$	52.40	913,320		$	52.80	833,630		$	49.92
Granted	260,000		55.71		245,000		49.46		232,500		59.41
Exercised	(57,055	)	44.53		(39,151	)	42.98		(149,060	)	46.97
Expired/Forfeited	(7,500	)	56.07		(5,000	)	54.78		(3,750	)	53.73
Outstanding December 31	1,309,614		53.38		1,114,169		52.40		913,320		52.80
Exercisable at December 31	763,614		52.43		600,919		50.93		430,945		48.94