HELENA, Mont. -

First Interstate Bank's parent company says it is acquiring Mountain West Bank in a deal that will pay Mountain West shareholders approximately $72.8 million.
    
First Interstate BancSystem Inc. senior vice president and marketing director Cynthia Lyle confirmed the acquisition announced Monday on First Interstate's website.
    
The deal must be approved by regulators and Mountain West shareholders.
    
Billings-based First Interstate says it expects those approvals by midyear.
    
Helena-based Mountain West Financial Corp. had $647 million in assets at the end of September and operates 12 branches in central and western Montana.
    
The merger would give First Interstate approximately $8.2 billion in assets. First Interstate Chairman Tom Scott says it gives the bank the chance to expand its Montana market.
    
First Interstate operates in Montana, Wyoming and South Dakota.