Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Net Income	$ 12,234	$ 12,725	$ 25,123	$ 29,636
Denominator:
Weighted average basic shares	28,171	26,745	28,194	26,730
Dilutive potential common shares	433	684	443	690
Weighted average fully diluted shares	28,604	27,429	28,637	27,420
Earnings per share:
Basic	$ 0.43	$ 0.48	$ 0.89	$ 1.11
Diluted	$ 0.43	$ 0.46	$ 0.88	$ 1.08
Outstanding common stock equivalents having no dilutive effect	184	131	184	131