Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic earnings per share
Net income available to common shareholders, Income	$ 70,672	$ 63,401	$ 52,580
Less: earnings allocated to participating securities, Income	(596)	(582)	(480)
Net income available to common shareholders, Total	$ 70,076	$ 62,819	$ 52,100
Net income available to common shareholders, (in shares)	50,477	47,578	47,438
Less: earnings allocated to participating securities, (in shares)	0	0	0
Net income available to common shareholders, Total (in shares)	50,477	47,578	47,438
Net income available to common shareholders, (in usd per share)	$ 1.40	$ 1.33	$ 1.11
Less: earnings allocated to participating securities, (in usd per share)	(0.01)	(0.01)	(0.01)
Net income available to common shareholders, Total (usd per share)	$ 1.39	$ 1.32	$ 1.10
Effect of dilutive securities
Stock options and restricted stock, Income	$ 0	$ 0	$ 0
Stock options and restricted stock, (in shares)	165	188	236
Stock options and restricted stock, (in usd per share)	$ (0.01)	$ 0	$ (0.01)
Diluted earnings per share
Net income available to common shareholders plus assumed conversions, Income	$ 70,076	$ 62,819	$ 52,100
Net income available to common shareholders plus assumed conversions, (in shares)	50,642	47,766	47,674
Net income available to common shareholders plus assumed conversions, (usd per share)	$ 1.38	$ 1.32	$ 1.09