Note 14 - Income Taxes - Effective Income Tax Rate Reconciliation (Details)		12 Months Ended
	Apr. 01, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax rate	19.00%	19.00%	19.00%
Valuation allowance				17.00%
Her Majesty's Revenue and Customs (HMRC) [Member]
Income tax rate		19.00%	19.00%
U.K. research and development credit		16.20%	1.80%
Permanent items		(6.10%)	1.00%
Prior period adjustments		5.90%	(5.20%)
State taxes		(19.00%)	9.20%
Other		(0.40%)	2.00%
Effect of foreign tax rate differential		(3.40%)	2.90%
Uncertain tax positions		2.50%	(1.70%)
Valuation allowance		49.60%	121.50%
Effective income tax rate		64.30%	150.50%