Note 5 - Credit Facilities (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest Expense, Debt, Total	$ 0.1	$ 0.1	$ 0.1
Line of Credit Maturing February 2022 [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 20.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.10%
Line of Credit Facility, Remaining Borrowing Capacity	$ 19.9	19.9
Letters of Credit Outstanding, Amount	0.1	0.1
Line of Credit Maturing May 2024 [Member]
Line of Credit Facility, Maximum Borrowing Capacity	6.5
Line of Credit Facility, Remaining Borrowing Capacity	2.0	3.1
Letters of Credit Outstanding, Amount	$ 4.5	4.9
Line of Credit Maturing May 2024 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	1.50%
Bank Guarantee [Member]
Line of Credit Facility, Maximum Borrowing Capacity		3.0
Line of Credit Facility, Remaining Borrowing Capacity	$ 1.2	1.5
Letters of Credit Outstanding, Amount	$ 1.8	$ 1.5
Line of Credit Facility, Interest Rate at Period End		1.75%