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, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic earnings per share
Net income available to common shareholders, Income	$ 63,401	$ 52,580	$ 41,518
Less: earnings allocated to participating securities, Income	(582)	(480)	(396)
Net income available to common shareholders, Total	$ 62,819	$ 52,100	$ 41,122
Net income available to common shareholders, Shares	47,578	47,438	42,912
Less: earnings allocated to participating securities, Shares	0	0	0
Net income available to common shareholders, Total	47,578	47,438	42,912
Net income available to common shareholders, Per share amount	$ 1.33	$ 1.11	$ 0.97
Less: earnings allocated to participating securities, Per share amount	(0.01)	(0.01)	(0.01)
Net income available to common shareholders, Total	$ 1.32	$ 1.10	$ 0.96
Effect of dilutive securities
Stock options and restricted stock, Income	$ 0	$ 0	$ 0
Stock options and restricted stock, Shares	188	236	202
Stock options and restricted stock, Per share amount	$ 0.00	$ (0.01)	$ (0.01)
Diluted earnings per share
Net income available to common shareholders plus assumed conversions, Income	$ 62,819	$ 52,100	$ 41,122
Net income available to common shareholders plus assumed conversions, Shares	47,766	47,674	43,114
Net income available to common shareholders plus assumed conversions, Per share amount	$ 1.32	$ 1.09	$ 0.95