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Note 12 - Employee Benefit Plans (Details Textual) - 401(k) Retirement Plan [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
UNITED STATES
Minimum Number Of Employee Working Hours Required To Be Eligible To Participate In 401K Plan	20
Minimum Service Period Of Employees To Avail Benefit Under Defined Contribution Benefit Plan	90 days
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	50.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 2.7	$ 1.9	$ 1.6
UNITED KINGDOM
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.3	$ 0.3	$ 0.2