Earnings Per Common Share - Summary of Earnings Per Common 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
Numerator for both basic and diluted earnings per common share:
Net income	$ 44,814	$ 33,169	$ 85,151	$ 66,698
Denominator:
Total average basic common shares outstanding	54,628,029	46,498,305	54,613,346	45,281,264
Effect of dilutive stock options and other stock compensation	105,492	141,475	110,863	135,746
Total diluted average common shares outstanding	54,733,521	46,639,780	54,724,209	45,417,010
Earnings per common share - basic	$ 0.82	$ 0.71	$ 1.56	$ 1.47
Earnings per common share - diluted	$ 0.82	$ 0.71	$ 1.56	$ 1.47