Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share Basic [Abstract]
Net income	$ 17,890	$ 16,956	$ 37,290	$ 33,125
Basic weighted average common shares	19,245,592	19,208,601	19,237,401	19,197,925
Basic earnings per common share	$ 0.93	$ 0.88	$ 1.94	$ 1.73
Net income	$ 17,890	$ 16,956	$ 37,290	$ 33,125
Weighted average common shares	19,245,592	19,208,601	19,237,401	19,197,925
Stock options and restricted stock	61,361	58,134	78,875	77,958
Diluted weighted average common shares	19,306,953	19,266,735	19,316,276	19,275,883
Diluted earnings per common share	$ 0.93	$ 0.88	$ 1.93	$ 1.72