Note 7 - Bank Credit Facility (Details Textual) - USD ($) $ in Thousands	Jun. 15, 2020	May 30, 2020
Bank One [Member]
Line of Credit Facility, Maximum Borrowing Capacity		$ 25,000
Letters of Credit Outstanding, Amount		4,773
Line of Credit Facility, Remaining Borrowing Capacity		20,227
Bank One [Member] | Subsequent Event [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 50,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Bank One [Member] | Subsequent Event [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	1.90%
Bank Two [Member]
Letters of Credit Outstanding, Amount		$ 325