Prospectus excerpt:  We are offering 12,500,000 shares of 6.50% Series I Cumulative Convertible Perpetual Preferred Stock. The annual dividend on each share of Series I preferred stock is $3.25 and is payable, when, as and if declared by our board of directors, quarterly in cash, in arrears, on each January 15, April 15, July 15 and October 15, commencing on July 15, 2011. Each share of Series I preferred stock has a liquidation preference of $50.00 per share and is convertible, at the holderĘs option at any time, initially into 0.8460 shares of our common stock (equal to an initial conversion price of approximately $59.10 per share), subject in each case to specified adjustments as set forth in this prospectus supplement. The Series I preferred stock is not redeemable by us. If a fundamental change occurs, we may be required to pay a make-whole premium on Series I preferred stock converted in connection therewith, as described in this prospectus supplement. On or after April 20, 2018, we may at our option cause all outstanding shares of the Series I preferred stock to be automatically converted into that number of shares of common stock for each share of Series I preferred stock equal to the then-prevailing conversion rate if the Daily VWAP of our common stock equals or exceeds 130% of the then-prevailing conversion price for at least 20 trading days in a period of 30 consecutive trading days, including the last trading day of such 30-day period.