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Loans Held for Investment - Schedule of Loans by Segment (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022 | Mar. 31, 2022 | Dec. 31, 2021
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Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Deferred loan fees and costs | $ (14.6) | $ (15.6) |  |
Loans held for investment, net of deferred fees and costs | 18,245.7 | 18,099.2 |  |
Allowance for credit losses | (226.1) | (220.1) | $ (247.2) | $ (122.3)
Net loans held for investment | 18,019.6 | 17,879.1 |  |
Nonaccrual loans | 37.5 | 39.8 |  |
Commercial real estate |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (78.6) | (74.6) | (125.0) | (43.9)
Financing Receivable, Loan in Process | 12.0 | 7.5 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 8,680.8 | 8,528.6 |  |
Nonaccrual loans | 28.2 | 19.6 |  |
Commercial real estate | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 10.2 | 5.6 |  |
Commercial real estate | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.6 | 0.8 |  |
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 | 0.2 | 1.1 |  |
Commercial real estate | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 8,640.6 | 8,501.5 |  |
Land acquisition & development |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (1.6) | (1.3) | (0.5) | (0.5)
Financing Receivable, Loan in Process | 3.5 | 2.4 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 368.5 | 386.2 |  |
Nonaccrual loans | 0.5 | 3.7 |  |
Land acquisition & development | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 3.2 | 1.8 |  |
Land acquisition & development | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.1 | 0.0 |  |
Land acquisition & development | 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 | 0.6 |  |
Land acquisition & development | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 364.5 | 380.1 |  |
Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (3.7) | (3.6) | (3.3) | (2.4)
Financing Receivable, Loan in Process | 0.4 | 1.1 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 471.4 | 516.2 |  |
Nonaccrual loans | 0.5 | 0.0 |  |
Residential | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.4 | 1.1 |  |
Residential | 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 |  |
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 | 0.0 |  |
Residential | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 470.5 | 515.1 |  |
Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (37.1) | (31.2) | (10.2) | (6.0)
Financing Receivable, Loan in Process | 0.6 | 8.1 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,053.1 | 1,042.0 |  |
Nonaccrual loans | 17.8 | 0.0 |  |
Commercial | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.6 | 7.5 |  |
Commercial | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.0 | 0.6 |  |
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 | 0.0 | 0.0 |  |
Commercial | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1,034.7 | 1,033.9 |  |
Total construction loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 4.5 | 11.6 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,893.0 | 1,944.4 |  |
Nonaccrual loans | 18.8 | 3.7 |  |
Total construction loans | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 4.2 | 10.4 |  |
Total construction loans | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.1 | 0.6 |  |
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 | 0.2 | 0.6 |  |
Total construction loans | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1,869.7 | 1,929.1 |  |
Residential |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (21.7) | (22.1) | (20.1) | (14.6)
Financing Receivable, Loan in Process | 7.0 | 13.2 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 2,191.1 | 2,188.3 |  |
Nonaccrual loans | 7.0 | 6.4 |  |
Residential | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 6.1 | 9.9 |  |
Residential | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.5 | 2.1 |  |
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 | 0.4 | 1.2 |  |
Residential | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2,177.1 | 2,168.7 |  |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (4.8) | (5.9) | (10.5) | (1.9)
Financing Receivable, Loan in Process | 7.5 | 7.2 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 769.7 | 794.9 |  |
Nonaccrual loans | 5.9 | 7.6 |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 7.2 | 1.1 |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.0 | 6.1 |  |
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 | 0.3 | 0.0 |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 756.3 | 780.1 |  |
Total real estate loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (147.5) | (138.7) | (169.6) | (69.3)
Financing Receivable, Loan in Process | 31.0 | 39.5 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 13,534.6 | 13,456.2 |  |
Nonaccrual loans | 59.9 | 37.3 |  |
Total real estate loans | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 27.7 | 27.0 |  |
Total real estate loans | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2.2 | 9.6 |  |
Total real estate 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 | 1.1 | 2.9 |  |
Total real estate loans | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 13,443.7 | 13,379.4 |  |
Indirect consumer |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (14.8) | (15.3) | (13.5) | (14.3)
Financing Receivable, Loan in Process | 8.1 | 12.3 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 817.3 | 829.7 |  |
Nonaccrual loans | 2.7 | 2.7 |  |
Indirect consumer | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 6.1 | 9.3 |  |
Indirect consumer | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1.6 | 2.4 |  |
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 | 0.4 | 0.6 |  |
Indirect consumer | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 806.5 | 814.7 |  |
Direct and advance lines |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (4.5) | (5.2) | (4.6) | (4.6)
Financing Receivable, Loan in Process | 1.1 | 1.2 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 146.9 | 152.9 |  |
Nonaccrual loans | 0.2 | 0.3 |  |
Direct and advance lines | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.7 | 0.8 |  |
Direct and advance lines | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.3 | 0.3 |  |
Direct and advance lines | 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 | 0.1 |  |
Direct and advance lines | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 145.6 | 151.4 |  |
Credit card |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (2.5) | (2.8) | (2.3) | (2.2)
Financing Receivable, Loan in Process | 1.5 | 1.8 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 71.5 | 75.9 |  |
Nonaccrual loans | 0.0 | 0.0 |  |
Credit card | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.5 | 0.8 |  |
Credit card | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.4 | 0.4 |  |
Credit card | 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 | 0.6 |  |
Credit card | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 70.0 | 74.1 |  |
Total consumer loans |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (21.8) | (23.3) | (20.4) | (21.1)
Financing Receivable, Loan in Process | 10.7 | 15.3 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1,035.7 | 1,058.5 |  |
Nonaccrual loans | 2.9 | 3.0 |  |
Total consumer loans | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 7.3 | 10.9 |  |
Total consumer loans | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2.3 | 3.1 |  |
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 | 1.1 | 1.3 |  |
Total consumer loans | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 1,022.1 | 1,040.2 |  |
Commercial |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (54.4) | (54.9) | (58.2) | (31.6)
Financing Receivable, Loan in Process | 13.9 | 10.9 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 3,028.0 | 2,882.6 |  |
Nonaccrual loans | 12.8 | 10.2 |  |
Commercial | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 9.4 | 7.1 |  |
Commercial | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 2.6 | 1.7 |  |
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 | 1.9 | 2.1 |  |
Commercial | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 3,001.3 | 2,861.5 |  |
Agricultural |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Allowance for credit losses | (2.4) | (3.2) | $ 1.0 | $ (0.3)
Financing Receivable, Loan in Process | 1.2 | 3.1 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 660.4 | 708.3 |  |
Nonaccrual loans | 5.2 | 8.7 |  |
Agricultural | 30 to 59 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.1 | 0.8 |  |
Agricultural | 60 to 89 Days Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.7 | 2.2 |  |
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 | 0.4 | 0.1 |  |
Agricultural | Financial Asset, Not Past Due |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 654.0 | 696.5 |  |
Other, including overdrafts |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 0.0 | 0.0 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 1.6 | 9.2 |  |
Nonaccrual loans | 0.0 | 0.0 |  |
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 | 1.6 | 9.2 |  |
Loans And Leases Held For Investment [Member] |  |  |  |
Loans and Leases Receivable Recorded Investment, Past Due [Line Items] |  |  |  |
Financing Receivable, Loan in Process | 56.8 | 68.8 |  |
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss | 18,260.3 | 18,114.8 |  |
Nonaccrual loans | 80.8 | 59.2 |  |
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 | 44.5 | 45.8 |  |
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 | 7.8 | 16.6 |  |
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 | 4.5 | 6.4 |  |
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 | $ 18,122.7 | $ 17,986.8 |  |

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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/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI https://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 https://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 https://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + 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 -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 3 -URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5066-111524 + Details
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