Supplementary Financial Data (Unaudited) - Schedule of Supplementary Financial Data (Unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 43,032	$ 40,468	$ 41,085	$ 42,039	$ 39,034	$ 37,982	$ 38,496	$ 34,349	$ 166,624	$ 149,861	$ 123,212
Gross profit	36,074	33,392	33,930	34,892	32,107	31,471	31,331	29,896	138,288	124,805	109,888
Net income	8,094	7,064	7,311	8,616	7,840	7,990	7,415	5,720	31,085	28,965	22,669
Net income available to common shareholders-basic	7,973	6,950	7,182	8,478	7,717	7,857	7,286	5,633	30,582	28,496	22,302
Net income available to common shareholders-diluted	$ 7,973	$ 6,950	$ 7,185	$ 8,481	$ 7,720	$ 7,857	$ 7,286	$ 5,636	$ 30,582	$ 28,510	$ 22,302
Income per common share:
Basic	$ 0.21	$ 0.18	$ 0.19	$ 0.23	$ 0.21	$ 0.22	$ 0.20	$ 0.16	$ 0.81	$ 0.78	$ 0.63
Diluted	$ 0.20	$ 0.18	$ 0.18	$ 0.22	$ 0.20	$ 0.21	$ 0.19	$ 0.15	$ 0.78	$ 0.76	$ 0.61