Note 15 - Income Taxes - Reconciliation of Statutory and Effective Tax Rates (Details)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
U.S. statutory rate		21.00%	21.00%	35.00%
State taxes		4.30%	4.70%	4.10%
State tax rate differential		(1.00%)
Research and development credits		(0.80%)	(1.30%)	(1.40%)
State credits		(1.00%)	(1.00%)	(0.20%)
Share-based compensation	[1]	(0.60%)	(0.50%)	(1.40%)
Tax Act impact (2)	[2]		(0.20%)	(13.90%)
Other		(0.80%)	(0.20%)	(0.90%)
Effective tax rate		21.10%	22.50%	21.30%

[1] With the adoption of ASU 2016-09 in 2017, excess tax benefits from equity awards are reflected within the provision for income taxes rather than within the consolidated balance sheet.

[2] As a result of the Tax Act, we recognized a one-time, non-cash benefit of $28.4 million in the fourth quarter of 2017 primarily from the impact of the revaluation of our net deferred tax liabilities. This non-cash benefit resulted primarily from the Federal rate reduction from 35% to 21%.