Organic growth is key to $4.8B firm's success

Summary: Ballentine Partners is among the fastest-growing RIAs in the country, and it's one of the few that has built its business organically and without relying on institutional clients to juice its assets. In the past four years, the Waltham, Mass.-based multifamily office has nearly doubled assets under management to $4.8 billion, from $2.5 billion in 2010. In the last year alone, it increased AUM by 25%, according to data collected by InvestmentNews.