Earnings per Common Share - Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic
Net income	$ 9,642	$ 7,682	$ 29,564	$ 22,019
Less allocation of earnings and dividends to participating securities	46	26	122	64
Net income available to common shareholders—basic	$ 9,596	$ 7,656	$ 29,442	$ 21,955
Weighted average common shares outstanding	15,168,233	16,045,544	15,543,488	16,201,898
Less average participating securities	72,071	54,274	64,064	47,246
Weighted average number of shares outstanding used in the calculation of basic earnings per common share	15,096,162	15,991,270	15,479,424	16,154,652
Earnings per common share:
Basic	$ 0.64	$ 0.48	$ 1.90	$ 1.36
Diluted	$ 0.64	$ 0.48	$ 1.90	$ 1.36