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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net income	$ 10,512	$ 11,049	$ 9,047	$ 8,493	$ 9,376	$ 10,832	$ 7,105	$ 5,681	$ 39,101	$ 32,994	$ 27,557
Weighted-average basic common shares outstanding									31,891	30,327	31,267
Stock options									2,699	2,589	1,887
Denominator for diluted earnings per share - Adjusted weighted-average shares	35,348	34,764	34,290	33,948	33,421	32,986	32,769	32,530	34,590	32,916	33,154
Basic									$ 1.23	$ 1.09	$ 0.88
Diluted	$ 0.30	$ 0.32	$ 0.26	$ 0.25	$ 0.28	$ 0.33	$ 0.22	$ 0.17	$ 1.13	$ 1.00	$ 0.83