BUTTE, Mont. and SIOUX FALLS, S.D., Feb. 12, 2019 /PRNewswire/ -- NorthWestern Corporation d/b/a NorthWestern Energy (NYSE: NWE) reported financial results for the year ended December 31, 2018. Net income for the period increased 21 percent to $197.0 million, or $3.92 per diluted share,...