Prospectus excerpt:  We are offering to the public 7,000,000 of our 8.00% Series B Fixed-to-Floating Rate Cumulative Redeemable Preferred Shares of Beneficial Interest, $0.01 par value per share, which we refer to in this prospectus supplement as the Series B Preferred Shares. This is an original issuance of the Series B Preferred Shares. From, and including, the date of original issuance to, but not including, June 15, 2024, we will pay cumulative dividends on the Series B Preferred Shares at a fixed rate of 8.00% per annum based on the $25.00 per share liquidation preference, or $2.00 per share. From, and including, June 15, 2024 and thereafter, we will pay cumulative dividends on the Series B Preferred Shares at a floating rate equal to three-month LIBOR (as defined herein) as calculated on each applicable dividend determination date (as defined herein) plus a spread of 5.99% per annum based on the $25.00 per share liquidation preference. We will pay quarterly cumulative dividends on the Series B Preferred Shares, in arrears, on the 15th day of each March, June, September and December, commencing on September 15, 2017 (provided that if any dividend payment date is not a business day, then the dividend that would otherwise have been payable on that dividend payment date may be paid on the next succeeding business day).