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Loans and Allowance for Credit Losses - Additional Information (Details) |  |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | ---
May 01, 2025 USD ($) | Apr. 01, 2024 USD ($) | Sep. 30, 2025 USD ($) segment portfolio | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) segment portfolio | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |  |
Loan participations |  |  | $ 4,000,000,000.0 |  | $ 4,000,000,000.0 |  |
Loan participations sold |  |  | 2,200,000,000 |  | 2,200,000,000 |  |
Loan participations retained |  |  | $ 1,800,000,000 |  | $ 1,800,000,000 |  |
Number of loan portfolios | portfolio |  |  | 4 |  | 4 |  |
Number of loan segments | segment |  |  | 7 |  | 7 |  |
Allowance for credit losses at acquisition |  | $ 26,700,000 |  |  |  |  |
Provision for credit losses |  |  | $ 26,738,000 | $ 28,497,000 | $ 164,976,000 | $ 83,602,000 |
Loan placed on nonaccrual when past due, number of days |  |  |  |  | 90 days |  |
Payment defaults |  |  | 0 | $ 3,900,000 | $ 16,900,000 | 25,300,000 |
Unfunded commitments on TDRs |  |  | 0 |  | 0 |  | $ 0
CapStar Financial Holdings, Inc. |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |  |
Allowance for credit losses at acquisition |  | $ 26,725,000 |  |  |  |  |
Provision for credit losses |  |  |  |  | 69,100,000 |  |
Accrued interest receivable on loans |  |  | 226,600,000 |  | $ 226,600,000 |  | $ 171,600,000
Bremer |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |  |
Allowance for credit losses at acquisition | $ 103,546,000 |  | $ 103,500,000 |  |  |  |
Provision for credit losses |  |  |  |  |  | 15,300,000 |
Bremer | Financial Asset Acquired with Credit Deterioration |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |  |
Allowance for credit losses at acquisition |  |  |  |  |  | $ 26,700,000 |
Commercial real estate |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |  |
Percentage of risk-based capital |  |  | 253.00% |  | 253.00% |  |
Regulatory guideline limit |  |  | 300.00% |  | 300.00% |  |

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