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An affiliate of Fidelity Investments has reacquired the 910,000-square-foot office building that’s served as Fidelity’s corporate headquarters since 2012 for $728.5 million.

Horizon Real Estate Investors LLC purchased 245 Summer St. and Fidelity signed a 20-year lease for the entire building, which typically houses a workforce of approximately 3,000 employees.

The sales price is just over $800 per square foot. U.S. Bank provided $684 million in mortgage financing for this week’s transaction.

Fidelity sold the property to University Park, Florida-based Benderson Development in 2004 for $307 million and leased back the office space. The 14-story building overlooking Fort Point Channel was originally completed in 1974 and sits on a 1.3-acre parcel.

In February, Turner Construction was issued a permit to conduct $5.3 million in renovations and utility work at the property, real estate newsletter Bldup reported.

Fidelity is simultaneously planning a 737,000-square-foot redevelopment of the Commonwealth Pier complex that it leases from Massport on Seaport Boulevard. The building’s exhibition hall will be demolished and 134,000 square feet of office space and 33,000 square feet of retail space will be added.

Fidelity spokesman Michael Aalto said the Commonwealth Pier project is moving forward, but is subject to the city of Boston’s current suspension of construction activity, so the company is assessing the effects on the project schedule.