Berkshire Hathaway Inc. is an American multinational conglomerate holding company headquartered in Omaha, Nebraska, United States. Its main business and source of capital is insurance, from which it invests the float (the retained premiums) in a broad portfolio of subsidiaries, equity positions and other securities. The company has been overseen since 1965 by its chairman and CEO Warren Buffett and (since 1978) vice chairman Charlie Munger, who are known for their advocacy of value investing principles. Under their direction, the company's book value has grown at an average rate of 20%, compared to about 10% from the S&P 500 index with dividends included over the same period, while employing large amounts of capital and minimal debt.