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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 11,851	$ 17,457	$ 24,243	$ 33,083
Less: earnings allocated to participating securities	108	147	211	287
Net income allocated to common shareholders	$ 11,743	$ 17,310	$ 24,032	$ 32,796
Weighted average number of common shares outstanding - basic (in shares)	50,522	50,509	50,554	50,393
Share-based plans (in shares)	71	140	107	151
Weighted average number of common shares outstanding - diluted (in shares)	50,593	50,649	50,661	50,544
Basic earnings per share (in usd per share)	$ 0.23	$ 0.34	$ 0.48	$ 0.65
Diluted earnings per share (in usd per share)	$ 0.23	$ 0.34	$ 0.47	$ 0.65