Note 6 - Investments - Net Changes in Unrealized Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investments	$ (3,758)	$ 3,132	$ 1,290	$ 1,984
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	(2,659)	(1,150)	(6,011)	9,990
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	(1,086)	4,455	6,251	(8,158)
Other investments
Gain (Loss) on Securities [Line Items]
Other Investments, Change in Unrealized Holding Gain (Loss)	$ (13)	$ (173)	$ 1,050	$ 152