In 1968, Mandelbaum contributed $250,000 towards the formation of Interstate Properties, a real estate development firm, with
Steven Roth and
Russell Wight. The firm later took control of the
Vornado fan company (previously acquired by the
Two Guys department store chain) and turned it into the
Vornado Realty Trust. Mandelbaum has been a trustee of the trust since 1979, and a Director of Alexander's, Inc. since 1995. In 2005, Mandelbaum and five other partners, in a group led by
Zygi Wilf, purchased the
Minnesota Vikings of the
National Football League from
Red McCombs for a reported 600 million.
Forbes estimates the 2014 value of the franchise at 1.007 billion, or 21st of the 32 NFL teams. Mandelbaum and his family were named 384th on the
Forbes 400 list in 2005, with an estimated net worth of $900 million. ==Family==