Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Data (Unaudited) [Abstract]
Revenues	$ 54,791	$ 56,681	$ 58,906	$ 50,273	$ 28,749	$ 34,745	$ 33,847	$ 34,741	$ 22,889	$ 27,861	$ 12,746	$ 6,575	$ 220,651	$ 132,082	$ 70,071
Gross profit	43,019	45,400	46,551	39,039	22,507	26,603	28,157	28,519	19,410	21,133	8,839	4,224	174,009	105,786	53,606
Net income (loss)	$ 5,894	$ 7,525	$ 4,213	$ 4,857	$ (2,983)	$ 4,249	$ (10,045)	$ 8,085	$ 2,929	$ 5,845	$ 1,876	$ 951	$ 22,489	$ (694)	$ 11,601
Net income (loss) per share
Basic (in dollars per share)	$ 0.28	$ 0.35	$ 0.20	$ 0.26	$ (0.22)	$ 0.34	$ (0.98)	$ 0.79	$ 0.29	$ 0.57	$ 0.18	$ 0.09	$ 1.10	$ (0.06)	$ 1.13
Diluted (in dollars per share)	$ 0.27	$ 0.35	$ 0.20	$ 0.26	$ (0.22)	$ 0.32	$ (0.98)	$ 0.68	$ 0.25	$ 0.50	$ 0.16	$ 0.08	$ 1.08	$ (0.06)	$ 0.99
Shares used in computing net income (loss) per share:
Basic (in shares)	20,947,985	21,205,675	20,547,244	18,339,977	13,509,866	12,341,723	10,256,364	10,256,364	10,256,364	10,256,364	10,256,364	10,256,364	20,355,520	11,602,049	10,256,364
Diluted (in shares)	21,356,819	21,752,845	21,034,814	18,876,163	13,509,866	13,182,818	10,256,364	11,819,587	11,794,422	11,760,412	11,719,104	11,664,900	20,764,354	11,602,049	11,724,569