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Commitments, Contingencies and Guarantees - Additional Information (Detail) - USD ($) | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Jun. 30, 2025 | Jan. 31, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
Commitments and Contingencies Disclosure [Line Items] |  |  |  |  |  |  |  |  |
ACL for off-balance sheet credit exposures | $ 7,721,000 | $ 4,138,000 | $ 7,721,000 | $ 4,138,000 | $ 8,221,000 |  | $ 4,138,000 | $ 4,138,000 | $ 5,088,000
Provision for off-balance sheet credit exposures | (500,000) | $ 0 | 0 | $ (950,000) |  |  |  |  |
Heartland Financial USA, Inc [Member] |  |  |  |  |  |  |  |  |
Commitments and Contingencies Disclosure [Line Items] |  |  |  |  |  |  |  |  |
ACL for off-balance sheet credit exposures |  |  |  |  |  | $ 3,600,000 |  |  |
Accrued Expenses and Taxes [Member] |  |  |  |  |  |  |  |  |
Commitments and Contingencies Disclosure [Line Items] |  |  |  |  |  |  |  |  |
ACL for off-balance sheet credit exposures | $ 7,700,000 |  | $ 7,700,000 |  |  |  | $ 4,100,000 |  |

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- Definition Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482454/460-10-45-1 + Details
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- Definition Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 220 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147476148/220-40-50-22 + Details
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