Complex sentence: The Seaport is currently owned and managed by the Howard Hughes Corporation, and formerly by General Growth Properties, who acquired the Seaport's longtime owner, the Rouse Company, in 2004.
Split into simpler sentences: The Seaport is currently owned and managed by The Howard Hughes Corporation. Formerly, it was run by General Growth Properties, who acquired the Seaport's longtime owner, The Rouse Company, in 2004.