Mack-Cali Realty Corp. decided to sell its entire suburban office portfolio spanning about 6.6 million square feet of space, with completion expected in 2020.

The real estate investment trust said it will initially sell two suburban office portfolios comprising roughly 2.4 million square feet in Parsippany and Madison, N.J., for approximately $285 million in cash and about $3.5 million of assumed lease obligations. Onyx Equities LLC and partners Taconic Capital Advisors LP and Axonic Capital LLC are acquiring the two portfolios, which represent about 36% of the square footage of the REIT's suburban holdings.

Mack-Cali aims to use the available sale proceeds to pay down its corporate-level, unsecured debt. The REIT said its entire holdings will comprise a waterfront class A office portfolio of roughly 5.0 million square feet and the Roseland multifamily operations once the suburban office portfolio sale is completed.

Mack-Cali said its board made the decision for the sale based on the recommendations of its strategic review committee comprising four independent directors and its financial advisers. The board will continue to review the committee's recommendations regarding available options for maximizing stockholder value.

Goldman Sachs & Co. LLC was the financial adviser to the strategic review committee.