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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income	$ 13,826	$ 11,777	$ 37,676	$ 43,629
Denominator:
Denominator for basic earnings per share–weighted average common shares	25,038	24,963	25,022	24,901
Effect of dilutive stock options	52	87	46	113
Effect of other common stock equivalents	568	505	557	511
Denominator for diluted earnings per share–adjusted weighted average common shares	25,658	25,555	25,625	25,525
Basic Earnings Per Share	$ 0.55	$ 0.47	$ 1.51	$ 1.75
Diluted Earnings Per Share	$ 0.54	$ 0.46	$ 1.47	$ 1.71