Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income	$ 28,195	$ 14,373	$ 79,601	$ 43,339
Denominator:
Denominator for basic earnings per share–weighted average common shares	25,792	25,527	25,752	25,494
Effect of dilutive stock options	167	152	168	124
Effect of other common stock equivalents	395	434	408	432
Denominator for diluted earnings per share–adjusted weighted average common shares	26,354	26,113	26,328	26,050
Basic Earnings Per Share	$ 1.09	$ 0.56	$ 3.09	$ 1.70
Diluted Earnings Per Share	$ 1.07	$ 0.55	$ 3.02	$ 1.67