Bermuda-based reinsurer Platinum Underwriters Holdings Ltd yesterday said it had added almost $140 million to the authorised amount under its existing share repurchase programme.The announcement takes the total authorised under the programme to $250 million.Platinum said the repurchases may be made in open market or privately negotiated transactions or otherwise, from time to time, depending on market conditions.The company also announced that the Board of Directors has declared a quarterly dividend of eight cents per common share. The dividend is payable on March 31, 2011 to shareholders of record on March 1, 2011.