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								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 8,618	$ 20,142	$ 18,836	$ 17,273	$ 15,317	$ 17,000	$ 14,740	$ 11,883	$ 64,869	$ 58,940	$ 39,101
Weighted-average basic common shares outstanding									34,137	33,011	31,891
Stock options									2,415	2,390	2,699
Denominator for diluted earnings per share - Adjusted weighted-average shares	37,864	36,349	36,097	35,895	35,661	35,284	35,161	35,500	36,552	35,401	34,590
Basic									$ 1.90	$ 1.79	$ 1.23
Diluted	$ 0.23	$ 0.55	$ 0.52	$ 0.48	$ 0.43	$ 0.48	$ 0.42	$ 0.33	$ 1.77	$ 1.66	$ 1.13