Newport Beach, California-based KBS Strategic Opportunity REIT has sold the 179,872-square-foot 50 Congress St. office building in Boston’s Financial District to Guggenheim Real Estate and Quincy-based Jumbo Capital Management for $79 million.

The 10-story building with ground-floor retail was designed by architects Andrews, Jaques & Rantoul as the headquarters for State Mutual Life Insurance and built between 1910 and 1915. It’s currently 90-percent leased to over 60 tenants including law firms, financial services and private equity firms and retail tenants.

“We executed on our business plan to refurbish the property, retain tenants and roll them to market, while driving up occupancy and rents in this great property,” KBS Senior Vice President of Acquisition and Asset Management Shep Wainwright said in a statement.

HFF’s Coleman Benedict, Christopher Phaneuf and Ben Sayles represented KBS in the transaction.

KBS paid $51 million to acquire the property in July 2013 from longtime owner Nordblom Co.