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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue	$ 153,497	$ 159,975	$ 139,761	$ 129,150	$ 129,430	$ 128,939	$ 112,198	$ 100,362	$ 582,382	$ 470,929	$ 388,665
Cost of revenue	68,904	70,957	62,197	57,655	58,269	58,083	50,773	45,520	259,714	212,646	177,792
Gross profit	84,593	89,018	77,564	71,495	71,161	70,856	61,425	54,842	322,668	258,283	210,873
Research and development	22,735	25,630	23,481	21,609	21,730	21,442	20,292	18,894	93,455	82,359	73,643
Selling, general and administrative	28,372	29,552	28,561	27,318	24,038	25,255	25,873	22,092	113,803	97,257	83,012
Litigation expense, net	409	343	640	531	340	327	290	286
Total operating expenses	51,516	55,525	52,682	49,458	46,108	47,024	46,455	41,272	209,180	180,859	156,426
Income from operations	33,077	33,493	24,882	22,037	25,053	23,832	14,970	13,570	113,488	77,424	54,447
Interest and other income (expense), net	(393)	2,714	2,232	440	1,647	1,255	1,237	1,381	4,994	5,520	2,817
Income before income taxes	32,684	36,207	27,114	22,477	26,700	25,087	16,207	14,951	118,482	82,944	57,264
Income tax provision	5,046	4,639	2,908	621	14,629	1,445	1,193	474	13,214	17,741	4,544
Net income	$ 27,638	$ 31,568	$ 24,206	$ 21,856	$ 12,071	$ 23,642	$ 15,014	$ 14,477	$ 105,268	$ 65,203	$ 52,720
Earnings per share, basic (in dollars per share)	$ 0.65	$ 0.75	$ 0.57	$ 0.52	$ 0.29	$ 0.57	$ 0.36	$ 0.35	$ 2.49	$ 1.58	$ 1.30
Earnings per share, diluted (in dollars per share)	$ 0.61	$ 0.71	$ 0.55	$ 0.49	$ 0.27	$ 0.54	$ 0.35	$ 0.33	$ 2.36	$ 1.50	$ 1.26
Weighted-average shares outstanding, basic (in shares)	42,467	42,362	42,237	41,922	41,574	41,458	41,323	41,047
Weighted-average shares outstanding, diluted (in shares)	45,058	44,669	44,400	44,282	44,610	43,486	43,397	43,268	44,602	43,578	41,915