Income and Dividends Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Income per share of common stock:
Net income for basic and diluted income per common share	$ 19,712	$ 17,104	$ 10,238	$ 8,668	$ 36,816	$ 18,906
Weighted-average shares for basic income per common share (in shares)	5,692		5,672		5,688	5,670
Effect of dilutive securities:
Employee and director stock options (in shares)	14		8		14	9
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,706		5,680		5,702	5,679
Basic net income per common share (in dollars per share)	$ 3.46		$ 1.80		$ 6.47	$ 3.33
Diluted net income per common share (in dollars per share)	3.45		1.80		6.46	3.33
Cash dividends per share of common stock (in dollars per share)	$ 0.20		$ 0.20		$ 0.40	$ 0.40
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	0		17		0	14