Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share Basic [Abstract]
Net income	$ 19,400	$ 16,169
Basic weighted average common shares	19,229,134	19,187,136
Basic earnings per common share	$ 1.01	$ 0.84
Net income	$ 19,400	$ 16,169
Weighted average common shares	19,229,134	19,187,136
Stock options and restricted stock	68,902	75,101
Diluted weighted average common shares	19,298,036	19,262,237
Diluted earnings per common share	$ 1.01	$ 0.84