Earnings Per Common Share - Summary of Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator for both basic and diluted earnings per common share:
Net income available to common shareholders	$ 70,584	$ 23,396
Denominator:
Total average basic common shares outstanding	67,263,714	67,486,550
Effect of dilutive stock options and other stock compensation	91,704	100,896
Total diluted average common shares outstanding	67,355,418	67,587,446
Earnings per common share - basic	$ 1.05	$ 0.35
Earnings per common share - diluted	$ 1.05	$ 0.35