Note 5 - Investments Net Unrealized Gains (Losses) on Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investments	$ 4,742	$ 820	$ 28,068	$ (15,538)
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	4,132	(2,581)	18,962	(18,431)
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	563	2,971	9,170	2,238
Other investments
Gain (Loss) on Securities [Line Items]
Other Investments, Change in Unrealized Holding Gain (Loss)	$ 47	$ 430	$ (64)	$ 655