Earnings Per Share - Computation of Basic Earnings and Diluted Earnings Per Share Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 15,317	$ 17,000	$ 14,740	$ 11,883	$ 10,512	$ 11,049	$ 9,047	$ 8,493	$ 58,940	$ 39,101	$ 32,994
Weighted-average basic common shares outstanding									33,011	31,891	30,327
Stock options									2,390	2,699	2,589
Denominator for diluted earnings per share - Adjusted weighted-average shares	35,661	35,284	35,161	35,500	35,348	34,764	34,290	33,948	35,401	34,590	32,916
Basic									$ 1.79	$ 1.23	$ 1.09
Diluted	$ 0.43	$ 0.48	$ 0.42	$ 0.33	$ 0.30	$ 0.32	$ 0.26	$ 0.25	$ 1.66	$ 1.13	$ 1.00