Net Income Per Common Share - Basic and Diluted Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share Reconciliation [Abstract]
Income available to common stockholders	$ 42,520	$ 22,608
Income available to common stockholders plus assumed exercises of stock options	$ 42,520	$ 22,608
Income available to common stockholders - Shares	32,756,852	32,679,587
Dilutive effect of stock options - Shares	651,264	607,772
Income available to common stockholders plus assumed exercises of stock options - Shares	33,408,116	33,287,359
Income available to common stockholders - Per Share Amount	$ 1.30	$ 0.69
Income available to common stockholders plus assumed exercises of stock options - Per Share Amount	$ 1.27	$ 0.68