Shares of Bermuda reinsurer White Mountains Insurance Group were up three percent yesterday after the company announced it had repurchased billionaire investor Warren Buffett’s $45 million stake in the company.White Mountains also revealed plans for self-tender offer that will allow investors to cash in shares at $500 each, the same price as was paid to Mr Buffett and more than $18 above Wednesday’s closing share price in New York. White Mountains intends to buy back up to one million shares through the offer.White Mountains’ shares at one point shot four percent beyond $500, but settled at $496.15, up $14.39, or 2.99 percent.Berkshire Hathaway Inc, Mr Buffett’s investment vehicle, sold 89,729 White Mountains shares back to the reinsurer.The company said it still has 30,668 shares remaining under its share repurchase authorisation.