Earnings Per Share - Calculation of Basic and Diluted Earnings Per 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
Earnings Per Share Basic [Abstract]
Net income	$ 19,136	$ 23,353	$ 62,215	$ 58,101
Basic weighted average common shares	19,344,636	19,299,921	19,328,041	19,282,263
Basic earnings per common share	$ 0.99	$ 1.21	$ 3.22	$ 3.01
Net income	$ 19,136	$ 23,353	$ 62,215	$ 58,101
Weighted average common shares	19,344,636	19,299,921	19,328,041	19,282,263
Restricted stock and stock options	63,282	58,761	64,898	63,689
Diluted weighted average common shares	19,407,918	19,358,682	19,392,939	19,345,952
Diluted earnings per common share	$ 0.99	$ 1.21	$ 3.21	$ 3.00