Cover |
Apr. 29, 2026 |
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| Cover [Abstract] | |
| Registrant Name | FIRST INTERSTATE BANCSYSTEM, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-34653 |
| Entity Tax Identification Number | 81-0331430 |
| Entity Address, Address Line One | 401 North 31st Street |
| Entity Address, State or Province | MT |
| Entity Address, City or Town | Billings, |
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- Definition Address Line 1 such as Attn, Building Name, Street Name No definition available.
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- Definition Name of the City or Town No definition available.
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- Definition Name of the state or province. No definition available.
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- Definition Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen. No definition available.
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- Definition Two-character EDGAR code representing the state or country of incorporation. No definition available.
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- Definition The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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