Note 4 - Accounts Receivable (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss, Current	$ 3.7	$ 3.9
Accounts Receivable, Credit Loss Expense (Reversal)	$ 0.6	$ 0.6	$ 0.6