Note 20 - Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue	$ 129,430	$ 128,939	$ 112,198	$ 100,362	$ 103,618	$ 106,456	$ 94,079	$ 84,512	$ 470,929	$ 388,665	$ 333,067
Cost of revenue	58,269	58,083	50,773	45,520	47,107	48,531	43,153	39,002	212,646	177,792	152,898
Gross profit	71,161	70,856	61,425	54,842	56,511	57,925	50,926	45,510	258,283	210,873	180,169
Research and development	21,730	21,442	20,292	18,894	17,974	20,472	17,876	17,321	82,359	73,643	65,787
Selling, general and administrative	24,038	25,255	25,873	22,092	21,316	22,397	21,531	17,768	97,257	83,012	72,312
Litigation expense, net	340	327	290	286	(321)	55	(8)	45
Total operating expenses	46,108	47,024	46,455	41,272	38,969	42,924	39,399	35,134	180,859	156,426	139,099
Income from operations	25,053	23,832	14,970	13,570	17,542	15,001	11,527	10,376	77,424	54,447	41,070
Interest and other income (expense), net	1,647	1,255	1,237	1,381	897	780	597	543	5,520	2,817	1,421
Income before income taxes	26,700	25,087	16,207	14,951	18,439	15,781	12,124	10,919	82,944	57,264	42,491
Income tax provision	14,629	1,445	1,193	474	1,866	1,408	926	344	17,741	4,544	7,319
Net income	$ 12,071	$ 23,642	$ 15,014	$ 14,477	$ 16,573	$ 14,373	$ 11,198	$ 10,575	$ 65,203	$ 52,720	$ 35,172
Earnings per share, basic (in dollars per share)	$ 0.29	$ 0.57	$ 0.36	$ 0.35	$ 0.41	$ 0.35	$ 0.28	$ 0.26	$ 1.58	$ 1.30	$ 0.89
Earnings per share, diluted (in dollars per share)	$ 0.27	$ 0.54	$ 0.35	$ 0.33	$ 0.39	$ 0.34	$ 0.27	$ 0.25	$ 1.50	$ 1.26	$ 0.86
Weighted-average shares outstanding, basic (in shares)	41,574	41,458	41,323	41,047	40,739	40,590	40,387	40,028
Weighted-average shares outstanding, diluted (in shares)	44,610	43,486	43,397	43,268	42,404	41,895	41,716	41,646	43,578	41,915	40,869
Common Stock, Dividends, Per Share, Declared	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.80	$ 0.80	$ 0.80