Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 18,874	$ 16,758	$ 51,957	$ 47,851
Less: earnings allocated to participating securities	156	153	443	440
Net income allocated to common shareholders	$ 18,718	$ 16,605	$ 51,514	$ 47,411
Weighted average number of common shares outstanding - basic (in shares)	50,553	47,605	50,447	47,570
Share-based plans (in shares)	141	183	148	194
Weighted average number of common shares outstanding - diluted (in shares)	50,694	47,788	50,595	47,764
Basic earnings per share (in usd per share)	$ 0.37	$ 0.35	$ 1.02	$ 1.00
Diluted earnings per share (in usd per share)	$ 0.37	$ 0.35	$ 1.02	$ 0.99