First Interstate BancSystem, parent company of First Interstate Bank, and Mountain West Financial Corp., parent company of Mountain West Bank, National Association announced that First Interstate has signed a definitive agreement to acquire the Helena-based Mountain West. With assets of $647M, as of September 30, 2013, Mountain West Bank currently operates 12 branches throughout central and western Montana in Helena, Great Falls, Missoula, Kalispell, Whitefish, and Bozeman. Upon completion of this merger, First Interstate will have total assets of approximately $8.2B and gain the number one deposit market share in the state of Montana. First Interstate expects the transaction to be immediately accretive to earnings per share. The transaction, unanimously approved by the boards of directors of both companies, is subject to regulatory approval and approval by the shareholders of Mountain West. Completion of the acquisition is expected by mid-2014.