A spokeswoman for the company tells GlobeSt.com that the plans are still new, and it's not clear what kind of retail will be added. She says more than 15 retailers are in negotiation for the property. "Our options are open," the spokeswoman says. "We are looking for the perfect tenants, whether they be big box stores, department stores or many small specialty retailers, and maybe an eatery."

She says since the retailers aren't chosen, it's not clear how much the addition would cost, though she says the average retail sales of stores on the property are at $460 per sf. The collection of 140 stores, known as the Hip in reference to the property's acronym, are currently 98% leased, and have been at least 95% leased for 20 years, the spokeswoman says.

The property started out as a 337,000-sf retail property with 45 tenants, and has already undergone several expansions. However, this new addition will mark the first time the mall will go outside the boundary of its original property. The adjacent parcel, sold by Bank of America Corp., includes a LaSalle Bank branch building and a parking lot. Construction on the new addition should start next fall, the spokeswoman says.