Earnings Per Common Share - Summary of Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator for both basic and diluted earnings per common share:
Net income available to common shareholders	$ 50,210	$ 41,305	$ 4,488	$ 23,396					$ 119,400	$ 158,873	$ 143,112
Denominator:
Total average basic common shares outstanding									67,260,796	56,108,084	48,889,041
Effect of dilutive stock options and other stock compensation									49,788	106,280	133,949
Total diluted average common shares outstanding									67,310,584	56,214,364	49,022,990
Earnings per common share—basic	$ 0.75	$ 0.61	$ 0.07	$ 0.34	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 1.78	$ 2.83	$ 2.93
Earnings per common share—diluted	$ 0.75	$ 0.61	$ 0.07	$ 0.34	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 1.77	$ 2.83	$ 2.92