Note 9 - Cash Equivalents, Investments and Restricted Cash (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total	$ 0	$ 0
Redemption, Auction Rate Securities to Date	$ 40,300
Percentage of Auction Rate Securities Redeemed at Par Value	93.00%
Equity Securities without Readily Determinable Fair Value, Amount	$ 3,180		$ 3,400