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Loans and Allowance for Credit Losses - Additional Information (Details)			3 Months Ended		6 Months Ended
	May 01, 2025 USD ($)	Apr. 01, 2024 USD ($)	Jun. 30, 2025 USD ($) segment portfolio	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) segment portfolio	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Loan participations			$ 4,200,000,000		$ 4,200,000,000
Loan participations sold			2,200,000,000		2,200,000,000
Loan participations retained			$ 2,000,000,000.0		$ 2,000,000,000.0
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			$ 106,835,000	$ 36,214,000	$ 138,238,000	$ 55,105,000
Loan placed on nonaccrual when past due, number of days					90 days
Payment defaults			4,600,000	27,000,000	$ 9,100,000	27,000,000
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		69,100,000
Accrued interest receivable on loans			193,400,000		$ 193,400,000		$ 171,600,000
Bremer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses at acquisition	$ 90,400,000	$ 90,442,000	$ 90,400,000
Provision for credit losses				15,300,000		$ 15,300,000
Bremer | Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses at acquisition				$ 23,900,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Percentage of risk-based capital			265.00%		265.00%
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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