Note 9 - Share Capital (Details Textual) $ / shares in Units, $ in Millions				12 Months Ended
	Jan. 30, 2015 USD ($)	Jan. 29, 2015 £ / shares shares	Jan. 29, 2015 £ / shares shares	Dec. 31, 2016 £ / shares shares	Dec. 31, 2015 £ / shares shares	Dec. 31, 2014 shares	Jan. 29, 2015 $ / shares shares
Common Stock, Par or Stated Value Per Share | £ / shares		£ 0.006705	£ 0.006705	£ 0.006705	£ 0.006705
Time Period for Underwriters to Exercise Share Grants from Date of Prospectus			30 days
Additional Shares Granted to Underwritten in Private Placement		638,297	638,297				638,297
Proceeds from Issuance of Private Placement, Gross | $	$ 57.5
Proceeds from Issuance of Private Placement | $	$ 53.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				85,943	41,222	65,054
Common Stock, Shares Authorized				36,183,293	36,183,293
Common Stock, Shares, Issued				22,635,431	22,549,488
Common Stock, Shares, Outstanding				22,635,431	22,549,488
Underwriters [Member]
Shares Issued, Price Per Share | $ / shares							$ 11.045
Private Placement [Member]
Stock Issued During Period, Shares, New Issues		4,255,319
Shares Issued, Price Per Share | $ / shares							$ 11.75