Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 17,457	$ 15,838	$ 33,083	$ 31,093
Less: earnings allocated to participating securities	147	146	287	287
Net income allocated to common shareholders	$ 17,310	$ 15,692	$ 32,796	$ 30,806
Weighted average number of common shares outstanding - basic (in shares)	50,509	47,600	50,393	47,552
Share-based plans (in shares)	140	170	151	201
Weighted average number of common shares outstanding - diluted (in shares)	50,649	47,770	50,544	47,753
Basic earnings per share (in usd per share)	$ 0.34	$ 0.33	$ 0.65	$ 0.65
Diluted earnings per share (in usd per share)	$ 0.34	$ 0.33	$ 0.65	$ 0.65