Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Apr. 30, 2021
Anti-dilutive securities
Common stock, authorized shares	15,000,000		30,000,000
Common stock, shares issued	5,653,336
Income per share of common stock:
Net income for basic and diluted income per common share	$ 7,031	$ 5,544
Weighted-average shares for basic income per common share (in shares)	5,651,000	5,624,000
Effect of dilutive securities:
Employee and director stock options (in shares)	13,000	10,000
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,664,000	5,634,000
Basic net income per common share (in dollars per share)	$ 1.24	$ 0.99
Diluted net income per common share (in dollars per share)	$ 1.24	$ 0.98
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	0	8,000