HM Insurance Group is going to acquire the stop-loss line of Mutual of Omaha, a move that catapults the subsidiary of Pittsburgh, Pa.-based Highmark Inc. to being one of the largest employer stop-loss carriers in the U.S.

Terms of the deal, which takes effect July 1, were not disclosed by either party.

“This acquisition will strengthen HM’s leadership position in the stop loss market,” said Michael W. Sullivan, president and chief operating officer of HM Insurance Group, in a statement. “The block complements our current stop-loss distribution channel, allows us to achieve greater economies of scale and supports our strategic direction as an expert in health risk solutions.”

Dan Martin, Mutual of Omaha’s executive vice president of group benefit services, said the deal was a “win-win transaction,” allowing his company to focus on continuing growth in its core product lines, while moving away from traditional health insurance.

Sullivan said the Mutual of Omaha stop-loss block, with about $100 million in annual premium, will increase HM’s current block of $420 million by nearly 25%. ”

MH intends to keep a regional stop-loss office in Omaha, Neb., where Mutual of Omaha’s company has been based, company officials said.

Through its insurance companies, HM Insurance Group holds insurance licenses in 50 states and Washington, D.C., and maintains 25 regional sales offices across the country