Net Income Per Common Share - Basic and Diluted Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share Reconciliation [Abstract]
Income available to common stockholders	$ 38,750	$ 20,890	$ 129,462	$ 64,228
Income available to common stockholders plus assumed exercises of stock options	$ 38,750	$ 20,890	$ 129,462	$ 64,228
Income available to common stockholders - Shares	32,744,104	32,668,789	32,760,015	32,666,554
Dilutive effect of stock options - Shares	523,851	500,149	598,822	523,740
Income available to common stockholders plus assumed exercises of stock options - Shares	33,267,955	33,168,938	33,358,837	33,190,294
Income available to common stockholders - Per Share Amount	$ 1.18	$ 0.64	$ 3.95	$ 1.97
Income available to common stockholders plus assumed exercises of stock options - Per Share Amount	$ 1.16	$ 0.63	$ 3.88	$ 1.94