Management buyout.

Duff & Phelps LLC, the Chicago-based investment bank with a longtime presence in Los Angeles, was purchased last week by a partnership of its management, Rolling Hills-based private equity group Lovell Minnick Partners LLC and New York investment bank Stone Ridge Partners.

Stone Ridge founder Noah Gottdiener will be chief executive of the combined firm, which will keep the Duff & Phelps name, said Greg Range, managing director of the Los Angeles office. Range is among the executives leading the purchase from publicly held Webster Financial Corp.

Duff & Phelps, which provides data for the LABJ 200 Index, is known for middle-market financial advisory and valuation services. It has 15 employees in its Los Angeles office.

Lovell Minnick founder Jeffrey Lovell said he has known Chet Gougis, president of Duff & Phelps, for more than 15 years. The purchase dovetailed with the firm's specialization in making equity investments of between $5 million and $30 million in non-bank financial services firms, Lovell said.

Its portfolio companies include investment advisor Stein Roe Investment Council, investment manager Arrowstreet Capital L.P. in Boston and Denali Advisors LLC in San Diego.

The transaction was initiated with Gougis and Gottdiener, a former partner at Thomas Weisel Partners who started Stone Ridge as an investment banking boutique. The two began looking for financing to arrange the buyout, Lovell said.

As part of the transaction, Stone Ridge will be merged into Duff & Phelps' New York office.