Banyan Partners, a fast-growing RIA based in Palm Beach Gardens, Fla., is acquiring Silver Bridge Advisors, the wealth management arm of global law firm WilmerHale. The transaction will more than double Banyan’s assets under management to about $3.5 billion.

The transaction provides Banyan CEO and founder Peter Raimondi with a platform to re-enter the Boston market. Raimondi co-founded the Colony Group in 1986 and ran that financial planning-oriented firm for 20 years. In September 2011, Focus Financial Partners acquired a majority interest in The Colony Group.

Prior to the Silver Bridge deal, Banyan had managed about $1.6 billion in assets. Silver Bridge manages about $1.9 billion directly and has just under another $1 billion in assets under advisement.

No purchase price was disclosed. However, sources said Silver Bridge wasn’t that profitable since WilmerHale viewed it as an ancillary service to offer clients. Consequently, Banyan may have received a very attractive price.

Raimondi said that he plans to retain all the Silver Bridge personnel and added that several will become Banyan principals, bringing the total number of equity shareholders in the firm to 25. “I believe that as many people as possible should own what they are building,” he said.

Scott Dell’Orfano, who joined Banyan as chief strategic officer earlier this year after spending eight years as executive vice president of Fidelity Institutional Wealth Services, agreed, noting that many RIA firm owners refuse to relinquish equity in a meaningful way and those who want to often don’t know how to structure it. “It is the number one reason why firms start flat-lining,” Dell’Orfano said.

In contrast to many RIA firms, Raimondi explained, Banyan is designed to be a customized asset manager with most of its assets managed internally rather than through third parties. Thomas Manning, CEO and CIO of Silver Bridge, will become CIO of Banyan and the firm’s current CIO, Michael Blackmon, will become executive director of portfolio management and supervise its 22 portfolio managers. “Tom will develop investment policy,” Raimondi said.

Banyan outsources management of only about $200 million in assets, much of it in the alternatives area. Raimondi explained that Banyan possesses internal asset management capabilities for a broad cross-section of investment strategies and is active in the options market.

Both Banyan and Silver Bridge have a handful of clients with a net worth of $50 million or $100 million, although the vast majority lie in the $2 million to $10 million range. Despite Banyan’s focus on asset management, Raimondi acknowledged, Silver Bridge will expand the firm’s capabilities in tax and estate planning.

With the lone exception of Genspring, Banyan is the only RIA in Florida with more than $1 billion in assets under management. The firm now has 70 employees and 8 offices including one in San Francisco, which came when Silver Bridge acquired Family Office Partners in that city in 2010.

Silver Bridge was spawned about 80 years ago out of the estate planning group of the Boston law firm Hale & Dorr. After that firm was merged with the giant Washington, D.C.-based law firm, Wilmer Cutler & Pickering, management at WilmerHale apparently chose to focus on the legal business. One source said that WilmerHale generates over $1 billion in annual revenues, while SilverBridge accounts for between 1% and 2% of that total, and senior management in Washington, D.C. didn't have the same degree of interest in wealth management that the Bostonian lawyers did.