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Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Mar. 31, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023
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Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Deferred loan fees and costs | $ (10.0) |  | $ (11.1) |  |  |
Allowance for credit losses | (209.6) | $ (215.3) | (204.1) | $ (232.8) | $ (227.7) | $ (227.7)
Net loans held for investment | 16,143.8 |  | 17,640.8 |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.2 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 16,353.4 |  | 17,844.9 |  |  |
Nonaccrual loans | 130.3 |  | 56.9 |  |  |
30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Nonaccrual loans | 29.5 |  | 13.5 |  |  |
60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Nonaccrual loans | 9.7 |  | 6.2 |  |  |
Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Nonaccrual loans | 74.7 |  | 40.5 |  |  |
Commercial real estate |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 5.4 |  | 7.7 |  |  |
Nonaccrual loans | 81.0 |  | 55.4 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 8,750.9 |  | 9,263.2 |  |  |
Commercial real estate | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.9 |  | 4.9 |  |  |
Commercial real estate | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 4.4 |  | 2.8 |  |  |
Commercial real estate | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.0 |  |  |
Commercial real estate | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 8,664.5 |  | 9,200.1 |  |  |
Total construction loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 9.6 |  | 3.7 |  |  |
Nonaccrual loans | 4.0 |  | 3.3 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 1,004.6 |  | 1,244.6 |  |  |
Total construction loans | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 9.3 |  | 3.7 |  |  |
Total construction loans | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.3 |  | 0.0 |  |  |
Total construction loans | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Total construction loans | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 991.0 |  | 1,237.6 |  |  |
Residential |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 3.3 |  | 9.7 |  |  |
Nonaccrual loans | 16.1 |  | 15.4 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 2,157.5 |  | 2,191.6 |  |  |
Residential | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 1.8 |  | 6.6 |  |  |
Residential | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 1.5 |  | 2.7 |  |  |
Residential | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.4 |  |  |
Residential | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 2,138.1 |  | 2,166.5 |  |  |
Agricultural |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 6.4 |  | 10.4 |  |  |
Nonaccrual loans | 20.8 |  | 5.3 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 635.6 |  | 701.1 |  |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 5.1 |  | 7.6 |  |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 1.2 |  | 2.8 |  |  |
Agricultural | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.0 |  |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 608.4 |  | 685.4 |  |  |
Total real estate |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Allowance for credit losses | (148.7) | (146.0) | (139.4) | (139.7) | (152.9) | (160.1)
Financing Receivable, Loan in Process | 24.7 |  | 31.5 |  |  |
Nonaccrual loans | 121.9 |  | 79.4 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 12,548.6 |  | 13,400.5 |  |  |
Total real estate | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 17.1 |  | 22.8 |  |  |
Total real estate | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 7.4 |  | 8.3 |  |  |
Total real estate | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.2 |  | 0.4 |  |  |
Total real estate | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 12,402.0 |  | 13,289.6 |  |  |
Indirect consumer |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 9.7 |  | 11.7 |  |  |
Nonaccrual loans | 3.9 |  | 3.9 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 607.1 |  | 725.0 |  |  |
Indirect consumer | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 7.0 |  | 8.4 |  |  |
Indirect consumer | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 2.1 |  | 2.6 |  |  |
Indirect consumer | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.6 |  | 0.7 |  |  |
Indirect consumer | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 593.5 |  | 709.4 |  |  |
Total consumer loans |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Allowance for credit losses | (12.0) | (15.9) | (16.8) | (18.5) | (12.6) | (13.0)
Financing Receivable, Loan in Process | 10.9 |  | 15.0 |  |  |
Nonaccrual loans | 4.4 |  | 4.5 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 741.5 |  | 936.6 |  |  |
Total consumer loans | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 7.8 |  | 9.7 |  |  |
Total consumer loans | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 2.4 |  | 3.3 |  |  |
Total consumer loans | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.7 |  | 2.0 |  |  |
Total consumer loans | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 726.2 |  | 917.1 |  |  |
Commercial |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Allowance for credit losses | (42.9) | (46.3) | (38.9) | (69.2) | (58.0) | (50.2)
Financing Receivable, Loan in Process | 7.6 |  | 14.8 |  |  |
Nonaccrual loans | 44.4 |  | 33.5 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 2,529.9 |  | 2,829.4 |  |  |
Commercial | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 3.9 |  | 11.2 |  |  |
Commercial | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 3.2 |  | 3.0 |  |  |
Commercial | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.5 |  | 0.6 |  |  |
Commercial | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 2,477.9 |  | 2,781.1 |  |  |
Agricultural |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Allowance for credit losses | (6.0) | $ (7.1) | (9.0) | $ (5.4) | $ (4.2) | $ (4.4)
Financing Receivable, Loan in Process | 10.4 |  | 5.2 |  |  |
Nonaccrual loans | 22.0 |  | 20.9 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 541.4 |  | 687.9 |  |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 10.4 |  | 2.4 |  |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 2.8 |  |  |
Agricultural | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 509.0 |  | 661.8 |  |  |
Other, including overdrafts |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Nonaccrual loans | 0.0 |  | 0.0 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 2.0 |  | 1.6 |  |  |
Other, including overdrafts | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Other, including overdrafts | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Other, including overdrafts | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.0 |  |  |
Other, including overdrafts | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 2.0 |  | 1.6 |  |  |
Loans And Leases Held For Investment [Member] |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 53.6 |  | 66.5 |  |  |
Nonaccrual loans | 192.7 |  | 138.3 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 16,363.4 |  | 17,856.0 |  |  |
Loans And Leases Held For Investment [Member] | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 39.2 |  | 46.1 |  |  |
Loans And Leases Held For Investment [Member] | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 13.0 |  | 17.4 |  |  |
Loans And Leases Held For Investment [Member] | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 1.4 |  | 3.0 |  |  |
Loans And Leases Held For Investment [Member] | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 16,117.1 |  | 17,651.2 |  |  |
Consumer Loan |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 1.2 |  | 1.1 |  |  |
Nonaccrual loans | 0.5 |  | 0.6 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 134.4 |  | 134.0 |  |  |
Consumer Loan | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.8 |  | 0.6 |  |  |
Consumer Loan | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.3 |  | 0.2 |  |  |
Consumer Loan | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.1 |  | 0.3 |  |  |
Consumer Loan | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 132.7 |  | 132.3 |  |  |
Credit Card Receivable [Member] |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 2.2 |  |  |
Nonaccrual loans | 0.0 |  | 0.0 |  |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process | 0.0 |  | 77.6 |  |  |
Credit Card Receivable [Member] | 30 to 59 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.7 |  |  |
Credit Card Receivable [Member] | 60 to 89 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 0.5 |  |  |
Credit Card Receivable [Member] | Equal to or Greater than 90 Days Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | 0.0 |  | 1.0 |  |  |
Credit Card Receivable [Member] | Financial Asset, Not Past Due |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |  |  |
Financing Receivable, Loan in Process | $ 0.0 |  | $ 75.4 |  |  |

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- Definition Amortized cost excluding accrued interest, after allowance for credit loss, of financing receivable. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-1 + Details
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- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-5 + Details
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- Definition Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 + Details
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- 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 -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-3 + Details
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