Note 3 - Cash, Cash Equivalents, Investments and Restricted Cash (Details Textual) - USD ($) $ in Thousands	12 Months Ended			108 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Auction Rate Securities Maturities	28 years
Percentage of Auction Rate Securities Redeemed at Par Value				92.00%
Redemption, Auction Rate Securities to Date				$ 39,700
Auction Rate Securities [Member]
Redemption Auction Rate Securities	$ 2,000	$ 0	$ 0
Other than Temporary Impairment Losses, Investments, Total	$ 300	$ 300