Permira, the investment fund that took over Dr. Martens and its parent company Airwear International from the Griggs family six years ago, is planning to cash out with a fat return on the investment, according to Sky News. It is reportedly seeking a valuation that would be more than double its original investment of £300 million (€347m-$390m) in view of the strong progress of the brand in recent years. The floating of the British company on a U.S. stock exchange is said to be a likely option.