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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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Amount, before allowance for credit loss, of accrued interest on financing receivable.

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