Income and Dividends Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Income per share of common stock:
Net income for basic and diluted income per common share	$ 20,733	$ 19,712	$ 17,104	$ 15,726	$ 10,238	$ 8,668	$ 57,549	$ 34,632
Weighted-average shares for basic income per common share (in shares)	5,696			5,674			5,691	5,671
Effect of dilutive securities:
Employee and director stock options (in shares)	16			6			14	8
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,712			5,680			5,705	5,679
Basic net income per common share (in dollars per share)	$ 3.64			$ 2.77			$ 10.11	$ 6.11
Diluted net income per common share (in dollars per share)	3.63			2.77			10.09	6.10
Cash dividends per share of common stock (in dollars per share)	$ 0.20			$ 0.20			$ 0.60	$ 0.60
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	0			17			0	14