Under the all-stock deal, NorthWestern shareholders will receive 0.98 Black Hills share for each held. This per-share value of $59.14 gives NorthWestern an equity value of $3.6 billion, according to Reuters' calculation.

The utility will have a market capitalization of approximately $7.8 billion, based on each company’s closing stock price as of Monday.

NorthWestern shareholders will receive 0.98 shares of Black Hills for each held. Black Hills stockholders would own roughly 56% of the company after the deal closes, which is expected in 12 to 15 months.