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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net Income	$ 14,426	$ 11,413	$ 39,549	$ 41,049
Denominator:
Weighted average basic shares	27,721	27,182	28,035	26,882
Dilutive potential common shares	511	744	468	710
Weighted average fully diluted shares	28,232	27,926	28,503	27,592
Earnings per share:
Basic	$ 0.52	$ 0.42	$ 1.41	$ 1.53
Diluted	$ 0.51	$ 0.41	$ 1.39	$ 1.49
Outstanding common stock equivalents having no dilutive effect	83	131	184	131