Madison Dearborn Partners, a Chicago-based private equity investment firm, completed the acquisition of an additional stake in Amynta Group, an insurance services company, from AmTrust Financial Services, a multinational property and casualty insurer. Financial terms were not disclosed. "MDP has been a great partner for Amynta and we will continue to value their expertise, insight and support of our vision and commitment as we embark on our next chapter of growth. The increased investment from MDP will foster the ability to drive the continued expansion of our business. We are grateful for AmTrust's strong support and value-added partnership since Amynta's formation and look forward to building on our very successful commercial relationship, delivering strong capacity to the market," Rob Giammarco, Amynta Chairman and CEO.