Shares of Greenhill & Co. (NYSE: GHL) are surging on Tuesday, trading higher by about 15% as of 11 a.m. EDT after the investment bank announced a recapitalization plan that would effectively allow it to buy out most of its minority public shareholders.Under the plan, the company expects to issue $300 million of debt plus $20 million of equity, which will be used to refinance existing debt and buy back millions of shares of stock.