Note 6 - Investments - Net Changes in Unrealized Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investments	$ (2,085)	$ (25,250)
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	(8,089)	(2,034)
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	5,118	(24,020)
Other investments
Gain (Loss) on Securities [Line Items]
Other Investments, Change in Unrealized Holding Gain (Loss)	$ 886	$ 804