BISMARCK, N.D., Nov. 21, 2017 /PRNewswire/ -- MDU Resources Group, Inc. (NYSE: MDU ) announced today that its Board of Directors has directed senior management to explore reorganization to a holding company structure. The purpose of a potential reorganization would be to make Montana-Dakota Utilities Co. and Great Plains Natural Gas Co., which today are divisions of MDU Resources, into subsidiaries of the holding company, just as MDU Resources' other operating companies are wholly owned subsidiaries.