Stabilis Capital Management of New York is seeking a buyer for the Millennium I, II and III office buildings that it owns on the Schuylkill waterfront in Conshohocken.

Stabilis decided to sell the Washington Street properties after their biggest tenant, AmerisourceBergen Corp., announced that it plans to relocate when its lease expires in 2020, said Doug Rodio, who is marketing the buildings as co-head of real estate services firm HFF's Philadelphia office.

The drug distributor occupies about half of the three building' collective 200,000 square feet, Rodio said.

AmerisourceBergen said in June that it would move to a new headquarters to be built for the company at the so-called Sora West development site elsewhere in Conshohocken.

The Millennium buildings' next-biggest tenant is Kynetic, an e-commerce holding company majority-owned by tech entrepreneur Michael Rubin, Rodio said. Kynetic's holdings include retailers Fanatics, Rue La La, and ShopRunner.

The buildings were developed by King of Prussia-based O'Neill Properties Group. Stabilis, O'Neill's lender on the properties, took over the buildings last year, the Philadelphia Business Journal has reported.