Carlyle will acquire NSM Insurance Group from White Mountains Insurance Group, according to a news release.

The transaction values NSM at $1.775 billion.

NSM, based in Conshohocken, Pa., is an independent insurance brokerage that underwrites policies for behavioral healthcare and several other sectors. Founded in 1990, NSM typically manages all aspects of the placement process on behalf of its insurance carrier partners.

Carlyle, with its U.S. headquarters in Washington, D.C., is a global investment firm that deploys private capital across three business segments: global private equity, global credit and investment solutions. Founded in 1987, the firm targets companies in healthcare and many other industries.

White Mountains Insurance Group is a Bermuda-domiciled financial services holding company with multiple locations in New England.