Loans and Allowance for Credit Losses - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) loan	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)	Sep. 30, 2024 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 17,188,817,000		$ 17,188,817,000		$ 17,005,937,000
Loan premiums and discounts			4,100,000		7,200,000
Deferred origination costs and fees	8,100,000		8,100,000		9,600,000
Financing receivable, accrued interest excluded from amortized costs	81,100,000		81,100,000		78,800,000
Nonaccrual loans with no allowance for credit loss	6,800,000		6,800,000		1,700,000
Financing receivable, collateral dependent, amount	108,416,000		108,416,000		102,580,000
Provision for credit loss expense	15,180,000	$ 12,148,000	53,922,000	$ 33,453,000
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded commitments, allowance for credit loss	25,600,000		25,600,000		25,600,000
Reserve for unfunded commitments, expensed (released)	0	0	0	0
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in process of foreclosure, amount	3,400,000		$ 3,400,000		4,000,000
Commercial Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans experiencing financial difficulty, modified, subsequent default | loan			1			1
Loan modified and subsequently defaulted			$ 26,700,000			$ 23,000
OREO Received in Full or Partial Satisfaction of Loans | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed assets and other real estate owned	4,200,000		4,200,000		1,300,000
Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense	15,180,000	$ 12,148,000	53,922,000	$ 33,453,000
Loans, Excluding Acquired Loans | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense			$ 15,600,000
Number of credit relationships migrated to nonperforming | loan			2
Paycheck Protection Program Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 370,000		$ 370,000		$ 1,600,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan			1 year
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan			3 years