Note 5 - Investments Net Unrealized Gains (Losses) on Investment Securities (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Gain (Loss) on Securities [Line Items]
Net changes in unrealized gains (losses) on investment securities	[1]	$ 349	$ 2,694	$ (16,268)	$ 10,011
Equity securities
Gain (Loss) on Securities [Line Items]
Equity Securities, Change in Unrealized Holding Gain (Loss)	[1]	2,971	0	2,238	0
Trading Securities
Gain (Loss) on Securities [Line Items]
Trading Securities, Change in Unrealized Holding Gain (Loss)	[1],[2]	$ (2,622)	$ 2,694	$ (18,506)	$ 10,011

[1] Related only to securities still held at period end. All amounts shown are included in net gains (losses) on investments and other financial instruments. 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.

[2] Includes a de minimis amount of net changes in unrealized gains (losses) related to short-term securities.