Earnings Per Share - Computation of Basic Earnings and Diluted Earnings Per Share Data (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
Earnings Per Share [Abstract]
Net income	$ 18,836	$ 14,740	$ 36,109	$ 26,623
Weighted-average basic common shares outstanding	33,751	32,918	33,756	32,876
Stock options	2,346	2,243	2,340	2,413
Denominator for diluted earnings per share - Adjusted weighted-average shares	36,097	35,161	36,096	35,289
Basic	$ 0.56	$ 0.45	$ 1.07	$ 0.81
Diluted	$ 0.52	$ 0.42	$ 1.00	$ 0.75