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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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share Basic [Abstract]
Net income	$ 23,353	$ 21,386	$ 58,101	$ 58,676
Basic weighted average common shares	19,299,921	19,256,069	19,282,263	19,243,689
Basic earnings per common share	$ 1.21	$ 1.11	$ 3.01	$ 3.05
Net income	$ 23,353	$ 21,386	$ 58,101	$ 58,676
Weighted average common shares	19,299,921	19,256,069	19,282,263	19,243,689
Stock options and restricted stock	58,761	46,482	63,689	76,510
Diluted weighted average common shares	19,358,682	19,302,551	19,345,952	19,320,199
Diluted earnings per common share	$ 1.21	$ 1.11	$ 3.00	$ 3.04

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Incremental common shares attributable to share based payment arrangements stock options and restricted stock.

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