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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to common shareholders, Income	$ 13,723	$ 11,327	$ 39,405	$ 29,565
Less: earnings allocated to participating securities, Income	122	114	362	275
Net income allocated to common shareholders	$ 13,601	$ 11,213	$ 39,043	$ 29,290
Weighted average number of common shares outstanding - basic	47,466	44,439	47,429	42,211
Share-based plans	226	220	231	179
Weighted average number of common shares outstanding - diluted	47,692	44,659	47,660	42,390
Basic earnings per share	$ 0.29	$ 0.25	$ 0.82	$ 0.69
Diluted earnings per share	$ 0.29	$ 0.25	$ 0.82	$ 0.69