Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Operating real estate, accumulated depreciation	$ 2,395,195	$ 2,433,053
Assets of consolidated variable interest entities	109,987	644,990
Liabilities of consolidated variable interest entities	$ 107,215	$ 417,688
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	5,996,240	5,996,240
Preferred stock, shares issued (in shares)	42,580	41,200
Preferred stock, shares outstanding (in shares)	42,580	41,200
Preferred stock, liquidation preference	$ 1,064,500	$ 1,030,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	750,000,000	750,000,000
Common stock, shares issued (in shares)	421,387,540	425,646,380
Common stock, shares outstanding (in shares)	421,387,540	425,646,380