Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 16,170	$ 11,897	$ 45,109	$ 37,565
Average number of common shares outstanding	30,011	22,932	25,317	22,901
Effect of dilutive stock options and restricted stock	280	312	300	338
Average number of common shares outstanding used to calculate diluted earnings per share	30,291	23,244	25,617	23,239
Options excluded from diluted earnings per share because the effect of these options was antidilutive	10,000		10,000