Note 7 - Leases (Details Textual) $ in Thousands			1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 08, 2019 USD ($) ft²	Jan. 01, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Increase (Decrease) in Operating Lease Liabilities					$ (1,059)
UNITED KINGDOM
Decrease In Operating Lease Liabilities and Right-of-Use Assets, Non-cash			$ 486		$ 486
UNITED KINGDOM | Previous Accounting Guidance [Member]
Lessee, Operating Lease, Term of Contract				15 years	15 years
Mansfield, Massachusetts [Member]
Operating Lease, Remaining Lease Term	3 years 120 days
Operating Lease, Increase in Area | ft²	6,100
Increase in Operating Lease Liabilities and Right-of-Use Assets, Non-cash	$ 1,811				$ 1,811
NETHERLANDS
Decrease In Operating Lease Liabilities and Right-of-Use Assets, Non-cash				$ 48	$ 48
Accounting Standards Update 2016-02 [Member]
Increase (Decrease) in Operating Lease Liabilities		$ 5,197
Increase (Decrease) in Operating Lease Right-of-Use Assets		$ 4,816