In connection with the Company's third quarter 2015 regular dividend of $0.20 per share, the conversion rate for the 2016 Notes increased to 18.1426 shares of common stock per $1,000 principal amount effective July 6, 2015, the ex-dividend date for the regular quarterly dividend.
From Dec 2012 press release...
In connection with the special dividend, the conversion rate applicable to the convertible notes increased to 17.9580 shares of common stock per $1,000 principal amount of the convertible notes.