Quarterly Financial Results (Unaudited) (Details) (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 Results (Unaudited) [Abstract]
Total revenues	$ 97,465	$ 96,758	$ 94,167	$ 84,935	$ 83,128	$ 87,474	$ 81,796	$ 74,698	$ 373,325	$ 327,096	$ 262,439
Gross margin	33,124	33,863	30,598	25,514	25,772	28,227	26,757	22,647	123,099	103,403	81,134
Income from operations	8,586	10,346	7,538	5,208	7,038	7,537	6,554	4,955	31,678	26,084	18,532
Income before income taxes	8,590	10,257	7,402	5,249	7,021	7,449	6,527	4,988	31,497	25,985	18,645
Net income	$ 5,513	$ 7,234	$ 4,562	$ 4,123	$ 4,376	$ 5,142	$ 3,603	$ 2,986	$ 21,432	$ 16,107	$ 10,747
Basic net income per share (in dollars per share)	$ 0.18	$ 0.24	$ 0.15	$ 0.14	$ 0.14	$ 0.17	$ 0.12	$ 0.10	$ 0.71	$ 0.54	$ 0.39
Diluted net income per share (in dollars per share)	$ 0.17	$ 0.23	$ 0.14	$ 0.13	$ 0.14	$ 0.16	$ 0.12	$ 0.10	$ 0.67	$ 0.52	$ 0.37