XML 94 R81.htm IDEA: XBRL DOCUMENT
v3.22.4

Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | $ 39,800,000 |
Loans and Leases Receivable, Nonperforming, Accrual of Interest | 0 |
Impaired Financing Receivable, Interest Income, Accrual Method | 0 |
Commercial Real Estate Portfolio Segment [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 19,600,000 | $ 8,000,000.0
Loans and Leases Receivable, Collateral for Secured Borrowings | 8,528,600,000 | 3,971,500,000
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 5,600,000 | 1,100,000
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 800,000 | 1,000,000.0
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,100,000 | 600,000
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 7,500,000 | 2,700,000
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 8,501,500,000 | 3,960,800,000
Land Acquisition And Development Construction Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 3,700,000 | 700,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 386,200,000 | 247,800,000
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 159,200,000 | 113,800,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 117,900,000 | 41,800,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 29,700,000 | 34,200,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 17,000,000.0 | 15,400,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 11,100,000 | 20,200,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 29,100,000 | 21,200,000
Financing Receivable, Excluding Accrued Interest, Revolving | 22,200,000 | 1,200,000
Land Acquisition And Development Construction Financing Receivable [Member] | Pass |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 152,500,000 | 113,000,000.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 114,400,000 | 41,500,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 29,500,000 | 34,200,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 17,000,000.0 | 14,800,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 10,900,000 | 19,800,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 28,400,000 | 20,800,000
Financing Receivable, Excluding Accrued Interest, Revolving | 22,200,000 | 1,200,000
Land Acquisition And Development Construction Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,800,000 | 200,000
Land Acquisition And Development Construction Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Land Acquisition And Development Construction Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 0
Land Acquisition And Development Construction Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,400,000 | 200,000
Land Acquisition And Development Construction Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 380,100,000 | 246,900,000
Residential Real Estate Construction Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 0 | 0
Loans and Leases Receivable, Collateral for Secured Borrowings | 516,200,000 | 262,000,000.0
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 118,400,000 | 112,400,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 120,400,000 | 7,400,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 400,000 | 13,700,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 300,000 | 900,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 400,000 | 400,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 6,200,000 | 0
Financing Receivable, Excluding Accrued Interest, Revolving | 270,100,000 | 127,200,000
Residential Real Estate Construction Financing Receivable [Member] | Pass |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 118,400,000 | 112,400,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 119,900,000 | 7,000,000.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 400,000 | 13,700,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 300,000 | 900,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 400,000 | 0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 5,800,000 | 0
Financing Receivable, Excluding Accrued Interest, Revolving | 270,100,000 | 127,200,000
Residential Real Estate Construction Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,100,000 | 4,200,000
Residential Real Estate Construction Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Residential Real Estate Construction Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Residential Real Estate Construction Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,100,000 | 4,200,000
Residential Real Estate Construction Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 515,100,000 | 257,800,000
Commercial Real Estate Construction [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 0 | 0
Loans and Leases Receivable, Collateral for Secured Borrowings | 1,042,000,000 | 498,000,000.0
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 461,800,000 | 209,700,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 399,200,000 | 141,400,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 112,800,000 | 118,800,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 45,900,000 | 27,600,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 400,000 | 0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 0 | 500,000
Financing Receivable, Excluding Accrued Interest, Revolving | 21,900,000 | 0
Commercial Real Estate Construction [Member] | Pass |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 442,700,000 | 209,700,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 374,800,000 | 141,400,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 89,700,000 | 118,800,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 45,900,000 | 27,600,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 400,000 | 0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 0 | 500,000
Financing Receivable, Excluding Accrued Interest, Revolving | 10,600,000 | 0
Commercial Real Estate Construction [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 7,500,000 | 0
Commercial Real Estate Construction [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 0
Commercial Real Estate Construction [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Commercial Real Estate Construction [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 8,100,000 | 0
Commercial Real Estate Construction [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,033,900,000 | 498,000,000.0
Real Estate Construction Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 3,700,000 | 700,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 1,944,400,000 | 1,007,800,000
Real Estate Construction Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 10,400,000 | 4,400,000
Real Estate Construction Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 0
Real Estate Construction Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 0
Real Estate Construction Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 11,600,000 | 4,400,000
Real Estate Construction Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,929,100,000 | 1,002,700,000
Residential Mortgage [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 6,400,000 | 2,900,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 2,188,300,000 | 1,538,200,000
Residential Mortgage [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 9,900,000 | 3,000,000.0
Residential Mortgage [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,100,000 | 800,000
Residential Mortgage [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,200,000 | 100,000
Residential Mortgage [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 13,200,000 | 3,900,000
Residential Mortgage [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,168,700,000 | 1,531,400,000
Agricultural Real Estate Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 7,600,000 | 4,900,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 794,900,000 | 213,900,000
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 204,200,000 | 62,400,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 185,800,000 | 38,600,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 115,500,000 | 37,300,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 68,000,000.0 | 23,300,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 59,300,000 | 13,200,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 119,600,000 | 33,300,000
Financing Receivable, Excluding Accrued Interest, Revolving | 42,500,000 | 5,800,000
Agricultural Real Estate Financing Receivable [Member] | Pass |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 180,000,000.0 | 58,300,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 172,800,000 | 36,900,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 109,500,000 | 35,100,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 64,800,000 | 22,600,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 46,600,000 | 11,800,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 105,100,000 | 28,100,000
Financing Receivable, Excluding Accrued Interest, Revolving | 31,400,000 | 4,900,000
Agricultural Real Estate Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,100,000 | 1,900,000
Agricultural Real Estate Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 6,100,000 | 200,000
Agricultural Real Estate Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Agricultural Real Estate Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 7,200,000 | 2,100,000
Agricultural Real Estate Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 780,100,000 | 206,900,000
Real Estate Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 37,300,000 | 16,500,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 13,456,200,000 | 6,731,400,000
Real Estate Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 27,000,000.0 | 10,400,000
Real Estate Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 9,600,000 | 2,000,000.0
Real Estate Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,900,000 | 700,000
Real Estate Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 39,500,000 | 13,100,000
Real Estate Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 13,379,400,000 | 6,701,800,000
Indirect consumer |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 2,700,000 | 1,700,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 829,700,000 | 737,600,000
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 381,300,000 | 273,100,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 177,300,000 | 209,100,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 130,600,000 | 108,700,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 60,000,000.0 | 64,200,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 33,800,000 | 37,100,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 46,700,000 | 45,400,000
Financing Receivable, Excluding Accrued Interest, Revolving | 0 | 0
Indirect consumer | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 9,300,000 | 5,100,000
Indirect consumer | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,400,000 | 1,400,000
Indirect consumer | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 400,000
Indirect consumer | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 12,300,000 | 6,900,000
Indirect consumer | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 814,700,000 | 729,000,000.0
Other consumer |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 300,000 | 100,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 152,900,000 | 129,200,000
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 52,700,000 | 42,600,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 32,000,000.0 | 27,900,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 18,300,000 | 15,000,000.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 8,500,000 | 13,400,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 6,500,000 | 5,800,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 9,000,000.0 | 7,600,000
Financing Receivable, Excluding Accrued Interest, Revolving | 25,900,000 | 16,900,000
Other consumer | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 800,000 | 500,000
Other consumer | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 300,000 | 200,000
Other consumer | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 100,000 | 100,000
Other consumer | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,200,000 | 800,000
Other consumer | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 151,400,000 | 128,300,000
Credit card consumer |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 0 | 0
Loans and Leases Receivable, Collateral for Secured Borrowings | 75,900,000 | 64,900,000
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 178,100,000 | 139,600,000
Credit card consumer | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 800,000 | 600,000
Credit card consumer | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 400,000 | 200,000
Credit card consumer | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 600,000 | 500,000
Credit card consumer | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,800,000 | 1,300,000
Credit card consumer | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 74,100,000 | 63,600,000
Total consumer loans |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 3,000,000.0 | 1,800,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 1,058,500,000 | 931,700,000
Total consumer loans | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 10,900,000 | 6,200,000
Total consumer loans | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 3,100,000 | 1,800,000
Total consumer loans | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,300,000 | 1,000,000.0
Total consumer loans | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 15,300,000 | 9,000,000.0
Total consumer loans | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,040,200,000 | 920,900,000
Commercial Portfolio Segment [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 10,200,000 | 5,000,000.0
Loans and Leases Receivable, Collateral for Secured Borrowings | 2,882,600,000 | 1,475,500,000
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 7,100,000 | 4,900,000
Commercial Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 1,700,000 | 700,000
Commercial Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,100,000 | 1,100,000
Commercial Portfolio Segment [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 10,900,000 | 6,700,000
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,861,500,000 | 1,463,800,000
Agricultural Financing Receivable [Member] |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 8,700,000 | 1,600,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 708,300,000 | 203,900,000
Agricultural Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 800,000 | 700,000
Agricultural Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 2,200,000 | 0
Agricultural Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 100,000 | 0
Agricultural Financing Receivable [Member] | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 3,100,000 | 700,000
Agricultural Financing Receivable [Member] | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 696,500,000 | 201,600,000
Other, including overdrafts |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 0 | 0
Loans and Leases Receivable, Collateral for Secured Borrowings | 9,200,000 | 1,500,000
Other, including overdrafts | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Other, including overdrafts | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Other, including overdrafts | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Other, including overdrafts | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 0 | 0
Other, including overdrafts | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 9,200,000 | 1,500,000
Loans held for investment |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Non-accrual Loans | 59,200,000 | 24,900,000
Loans and Leases Receivable, Collateral for Secured Borrowings | 18,114,800,000 | 9,344,000,000
Loans held for investment | Financing Receivables, 30 to 59 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 45,800,000 | 22,200,000
Loans held for investment | Financing Receivables, 60 to 89 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 16,600,000 | 4,500,000
Loans held for investment | Financing Receivables, Equal to Greater than 90 Days Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 6,400,000 | 2,800,000
Loans held for investment | Financial Asset, Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 68,800,000 | 29,500,000
Loans held for investment | Financial Asset, Not Past Due |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Loan in Process | 17,986,800,000 | 9,289,600,000
Non Owner Occupied Loans |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 1,163,700,000 | 512,000,000.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 882,000,000.0 | 470,600,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 674,200,000 | 242,300,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 490,400,000 | 151,100,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 261,100,000 | 77,300,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 907,600,000 | 425,000,000.0
Financing Receivable, Excluding Accrued Interest, Revolving | 29,200,000 | 15,300,000
Non Owner Occupied Loans | Pass |  |
Loans and Leases Receivable Recorded Investment, Past Due |  |
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year | 1,162,600,000 | 507,900,000
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year | 861,300,000 | 452,200,000
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year | 661,100,000 | 237,900,000
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year | 467,600,000 | 150,400,000
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year | 241,500,000 | 76,300,000
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year | 890,400,000 | 409,000,000.0
Financing Receivable, Excluding Accrued Interest, Revolving | $ 29,200,000 | $ 15,300,000

X
- Definition Amount excluding accrued interest, before allowance for credit loss, of financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated more than five years prior to current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable that can be withdrawn, repaid, and redrawn. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestRevolving
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated four years prior to current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated three years prior to current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated in current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated two years prior to current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount excluding accrued interest of financing receivable originated in fiscal year prior to current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of undisbursed portion of financing receivable balance. Excludes financing receivable covered under loss sharing agreement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5066-111524 + Details
Name: | us-gaap_FinancingReceivableLoanInProcess
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of financing receivable on nonaccrual status. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 16 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (3) Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (2) + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524 + Details
Name: | us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Reflects the carrying amount of loans deemed to be questionable as to collection on which interest is continuing to be earned or accrued. + References No definition available. + Details
Name: | us-gaap_LoansAndLeasesReceivableImpairedNonperformingAccrualOfInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables30To59DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables60To89DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetNotPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_LandAcquisitionAndDevelopmentConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_PassMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_ResidentialRealEstateConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateConstructionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_RealEstateConstructionFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_AgriculturalRealEstateFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_RealEstateFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_ConsumerIndirectFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_AgriculturalFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_OtherFinancingReceivableIncludingOverdraftsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_LoansAndLeasesHeldForInvestmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fibk_CommercialRealEstateNonOwnerOccupiedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |