Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Agency securities pledged	$ 6,818,582	$ 7,094,766
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued (in shares)	42,335,000	41,877,000
Common stock, shares outstanding (in shares)	42,335,000	41,877,000
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	9,610,000
Preferred stock, dividend rate	8.25%	8.25%
Preferred stock, shares issued (in shares)	2,181,000	2,181,000
Preferred stock, shares outstanding (in shares)	2,181,000	2,181,000
Preferred stock, aggregate liquidation preference	$ 54,514	$ 54,514
Series B Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	7,650,000
Preferred stock, dividend rate	7.875%	7.875%
Preferred stock, shares issued (in shares)	6,369,000	6,262,000
Preferred stock, shares outstanding (in shares)	6,369,000	6,262,000
Preferred stock, aggregate liquidation preference	$ 159,232	$ 156,560
Credit Risk and Non-Agency Securities
Trading securities pledged	820,900	$ 974,372
US Treasury Securities
Trading securities pledged	$ 17,264