Note 15 - Employee Benefit Plans (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unites States Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 314,000	$ 277,000	$ 126,000
United Kingdom Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 685,000	$ 613,000	$ 636,000
Defined Contribution Plan Minimum Annual Contributions per Employee, Percent		5.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		5.00%