Note 5 - Investments Net Unrealized Gains (Losses) on Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investments	$ (25,250)	$ 16,506
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	(2,034)	8,587
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	(24,020)	7,919
Other investments
Gain (Loss) on Securities [Line Items]
Other Investments, Change in Unrealized Holding Gain (Loss)	$ 804	$ 0