Note 18 - Quarterly Financial Data (Unaudited) (Details) - USD ($) shares in Thousands, $ in Thousands	3 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
Product revenue	$ 25,607	$ 23,676	$ 22,898	$ 15,515	$ 17,880	$ 21,975	$ 21,267	$ 14,352
Total revenue	30,894	23,681	22,904	15,520	23,255	22,055	26,275	34,010
Cost of product revenue	6,290	5,176	5,274	4,313	5,511	5,725	5,333	4,361
Gross profit on product revenue	19,317	18,500	17,624	11,202	12,369	16,250	15,934	9,991
Net income	$ 11,042	$ 8,380	$ 7,820	$ 3,516	$ 7,816	$ 6,171	$ 9,302	$ 15,030
Basic net income per share (in dollars per share)	$ 0.74	$ 0.56	$ 0.52	$ 0.24	$ 0.53	$ 0.42	$ 0.63	$ 1.04
Basic common shares outstanding (in shares)	14,965	14,967	14,961	14,905	14,801	14,759	14,688	14,461
Diluted net income per share (in dollars per share)	$ 0.72	$ 0.55	$ 0.51	$ 0.23	$ 0.51	$ 0.40	$ 0.60	$ 0.97
Diluted common shares outstanding (in shares)	15,353	15,316	15,336	15,330	15,278	15,435	15,493	15,499