Things are heating up in the $1.8-billion packaged-ice business. Dallas-based Reddy Ice Holdings Inc. said Monday that Arizona's attorney general has joined Florida in demanding documents related to an ongoing antitrust investigation of the industry by the U.S. Department of Justice. Reddy Ice, which supplies major retailers throughout the Florida and other Sun Belt states, is the largest of three manufacturers that control about 70 percent of all ice sales. A federal lawsuit filed in March charged that Reddy, along with Arctic Glacier International of Canada and Home City Ice Co. of Cincinnati, conspired to fix prices and allocate markets to avoid competition. Florida's attorney general demanded documents from Reddy in late March. Since disclosure of the federal antitrust lawsuit, Reddy's share price has plummeted by nearly a third, closing Monday at $12.93, down 9 cents. A year ago, an investment fund offered to buy the company for $31.25 a share; that deal fell through in January.