Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except 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, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Data (Unaudited) [Abstract]
Revenues	$ 63,490	$ 45,893	$ 58,065	$ 57,216	$ 54,791	$ 56,681	$ 58,906	$ 50,273	$ 28,749	$ 34,745	$ 33,847	$ 34,741	$ 224,664	$ 220,651	$ 132,082
Gross profit	50,777	36,827	46,675	45,350	43,019	45,400	46,551	39,039	22,507	26,603	28,157	28,519	179,629	174,009	105,786
Net income (loss)	$ 3,185	$ 886	$ 7,094	$ 7,212	$ 5,894	$ 7,525	$ 4,213	$ 4,857	$ (2,983)	$ 4,249	$ (10,045)	$ 8,085	$ 18,377	$ 22,489	$ (694)
Net income (loss) per share
Basic (in dollars per share)	$ 0.16	$ 0.04	$ 0.34	$ 0.35	$ 0.28	$ 0.35	$ 0.20	$ 0.26	$ (0.22)	$ 0.34	$ (0.98)	$ 0.79	$ 0.90	$ 1.10	$ (0.06)
Diluted (in dollars per share)	$ 0.16	$ 0.04	$ 0.34	$ 0.34	$ 0.27	$ 0.35	$ 0.20	$ 0.26	$ (0.22)	$ 0.32	$ (0.98)	$ 0.68	$ 0.89	$ 1.08	$ (0.06)
Shares used in computing net income (loss) per share:
Basic (in shares)	19,400,341	19,982,967	20,573,048	20,678,023	20,947,985	21,205,675	20,547,244	18,339,977	13,509,866	12,341,723	10,256,364	10,256,364	20,454,970	20,355,520	11,602,049
Diluted (in shares)	19,602,611	20,441,262	21,033,349	21,147,583	21,356,819	21,752,845	21,034,814	18,876,163	13,509,866	13,182,818	10,256,364	11,819,587	20,657,240	20,764,354	11,602,049