Note 5 - Investments Net Unrealized Gains (Losses) on Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investments	$ 24,032	$ 9,150	$ (1,010)	$ 23,634
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	13,790	7,608	11,131	15,027
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	10,443	1,404	(12,612)	8,600
Other investments
Gain (Loss) on Securities [Line Items]
Other Investments, Change in Unrealized Holding Gain (Loss)	$ (201)	$ 138	$ 471	$ 7