Quarterly Financial Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Results (Unaudited) [Abstract]
Total revenues	$ 133,650	$ 120,909	$ 108,464	$ 110,598	$ 125,842	$ 116,971	$ 116,709	$ 97,170	$ 473,621	$ 456,692	$ 373,325
Gross margin	43,847	40,402	34,901	36,060	40,491	39,537	37,848	31,459	155,210	149,335	123,099
Income from operations	11,133	11,595	5,474	7,050	9,730	12,395	11,416	5,421	35,252	38,963	31,678
Income before income taxes	10,618	11,065	4,935	6,217	9,263	11,943	11,040	5,274	32,835	37,520	31,497
Net income	$ 7,570	$ 7,374	$ 3,997	$ 4,066	$ 6,424	$ 7,306	$ 6,387	$ 3,045	$ 23,007	$ 23,163	$ 21,432
Basic net income per share (in dollars per share)	$ 0.22	$ 0.22	$ 0.12	$ 0.12	$ 0.20	$ 0.23	$ 0.20	$ 0.10	$ 0.69	$ 0.73	$ 0.71
Diluted net income per share (in dollars per share)	$ 0.22	$ 0.22	$ 0.12	$ 0.12	$ 0.19	$ 0.22	$ 0.19	$ 0.09	$ 0.67	$ 0.70	$ 0.67