The 53-story office building is New York City’s largest office tower, spanning 3.8 million square feet bordered by Water and South streets and Old Slip at the southern tip of Manhattan.

The new lease more than doubles the insurer’s headquarters in the Financial District to 120,000 square feet. The company will be moving its offices from the 18th floor to the 22nd and 23rd floors. Liberty Mutual declined to comment on the expansion.