Income and Dividends Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Anti-dilutive securities
Common stock, authorized shares	30,000,000				30,000,000
Common stock, shares outstanding	5,673,610				5,673,610
Income per share of common stock:
Net income for basic and diluted income per common share	$ 10,238	$ 8,668	$ 11,093	$ 7,031	$ 18,906	$ 18,124
Weighted-average shares for basic income per common share (in shares)	5,672,000		5,657,000		5,670,000	5,654,000
Effect of dilutive securities:
Employee and director stock options (in shares)	8,000		12,000		9,000	13,000
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,680,000		5,669,000		5,679,000	5,667,000
Basic net income per common share (in dollars per share)	$ 1.80		$ 1.96		$ 3.33	$ 3.21
Diluted net income per common share (in dollars per share)	1.80		1.96		3.33	3.20
Cash dividends per share of common stock (in dollars per share)	$ 0.20		$ 0.16		$ 0.40	$ 0.32
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	17,000		0		14,000	0