Note 6 - Investments Net Unrealized Gains (Losses) on Investment Securities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investment securities		$ (25,348)	$ 8,827	$ 16,850
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	[1]	(8,886)	0	0
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)		$ (16,462)	$ 8,827	$ 16,850

[1] Prior to the implementation of the update to the standard for the accounting of financial instruments effective January 1, 2018, the unrealized losses associated with equity securities were classified in accumulated other comprehensive income.