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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 14,407	$ 13,826	$ 43,397	$ 37,676
Denominator:
Denominator for basic earnings per share–weighted average common shares	25,527	25,038	25,494	25,022
Effect of dilutive stock options	152	52	124	46
Effect of other common stock equivalents	434	568	432	557
Denominator for diluted earnings per share–adjusted weighted average common shares	26,113	25,658	26,050	25,625
Basic Earnings Per Share	$ 0.56	$ 0.55	$ 1.70	$ 1.51
Diluted Earnings Per Share	$ 0.55	$ 0.54	$ 1.67	$ 1.47