The Blackstone Group has completed its purchase of World Market Center. Fireside Investments partnered with Blackstone on the deal, which was unveiled in July. It is huge — spanning 5.4 million square feet. It hosts two industry gatherings per year that typically last a week and draw 45,000 attendees each. It opened in 2005 with one building. It expanded in 2007 with a second building and grew again in 2008 with a third.