Note 9 - Income Taxes Summary of Income Tax Examinations (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2018	Sep. 04, 2014	May 31, 2010	Jun. 30, 2008
Income Tax Examination [Line Items]
Income Tax Expense (Benefit)		$ 27,956	$ 38,198
REMIC Residual [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Qualified Deposit With The U.S. Department Of Treasury Relating to Tax Years 2000 Through 2004							$ 85,000
Qualified Deposit With The U.S. Department Of Treasury Relating To Tax Years 2005 Through 2007						$ 4,000
Income Tax Examination, Penalties Accrued					$ 157,000
Scenario, Forecast [Member]
Income Tax Examination [Line Items]
Reduction to Available Holding Company Liquidity				$ 35,000
Income Tax Expense (Benefit)	$ (30,000)