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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator for both basic and diluted earnings per common share:
Net income	$ 36,376	$ 37,347	$ 44,814	$ 40,337	$ 43,928	$ 32,486	$ 33,169	$ 33,529	$ 158,873	$ 143,112	$ 94,482
Denominator:
Total average basic common shares outstanding									56,108,084	48,889,041	44,003,208
Effect of dilutive stock options and other stock compensation									106,280	133,949	72,085
Total diluted average common shares outstanding									56,214,364	49,022,990	44,075,293
Earnings per common share—basic	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 0.80	$ 0.65	$ 0.71	$ 0.76	$ 2.83	$ 2.93	$ 2.15
Earnings per common share—diluted	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 0.80	$ 0.64	$ 0.71	$ 0.76	$ 2.83	$ 2.92	$ 2.14