Capital Stock

3 Months Ended

Mar. 31, 2026

Equity [Abstract]

Capital Stock

The Company’s common stock is traded on the NASDAQ stock market under the symbol “FIBK.”

As of March 31, 2026, the Company is authorized to issue an aggregate of 150,100,000 shares of capital stock, of which 150,000,000 shares are designated as common stock, and 100,000 are designated as preferred stock. Our common stock is uncertificated and has one vote per share.

The Company had 97,446,230 shares and 101,105,745 shares of common stock outstanding as of March 31, 2026 and December 31, 2025, respectively, and no shares of preferred stock outstanding as of March 31, 2026 and December 31, 2025.

On August 28, 2025, the board of directors of the Company adopted a new stock repurchase program, pursuant to which the Company has been authorized to repurchase up to $150.0 million of its issued and outstanding shares of common stock on or prior to March 31, 2027, which is the expiration date of the program. On January 27, 2026, the board of directors authorized an increase to the repurchase program of an additional $150.0 million, or a total of $300.0 million since August 2025. Any repurchased shares will be returned to authorized but unissued shares of common stock, as permitted under applicable Delaware law.

During the three months ended March 31, 2026, 2,392,893 shares of common stock were repurchased under the stock repurchase program at a total cost of $84.0 million or at a weighted average price of $35.09 per share. As of March 31, 2026, following these repurchases, approximately $98.4 million remained available for future purchases under the program. The additional stock repurchases during the three months ended March 31, 2026 and 2025, were redemptions of vested restricted shares tendered in lieu of cash for payment of income tax withholding amounts by participants in the Company’s equity compensation plans.