Note 5 - Investments Investments Trading Securities (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized Gain (Loss) on Trading Securities Held		$ (11,400)	$ 3,500
Trading Securities	[1]	563,409		$ 606,434
Unrealized Gain (Loss) on Equity Securities Held		(1,800)
State and municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		203,188		214,841
Corporate bonds and notes
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		280,323		307,271
RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		26,084		29,520
CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		49,634		50,561
Foreign government securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		$ 4,180		$ 4,241

[1] Includes a de minimis amount of loaned securities under securities lending agreements that are classified as other assets in our consolidated balance sheets, as further described below.