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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 14,427	$ 18,874	$ 38,670	$ 51,957
Less: earnings allocated to participating securities	131	156	342	443
Net income allocated to common shareholders	$ 14,296	$ 18,718	$ 38,328	$ 51,514
Weighted average number of common shares outstanding - basic (in shares)	50,526	50,553	50,544	50,447
Share-based plans (in shares)	94	141	101	148
Weighted average number of common shares outstanding - diluted (in shares)	50,620	50,694	50,645	50,595
Basic earnings per share (in usd per share)	$ 0.28	$ 0.37	$ 0.76	$ 1.02
Diluted earnings per share (in usd per share)	$ 0.28	$ 0.37	$ 0.76	$ 1.02