Loans and Allowance for Credit Losses - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($) loan	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($) loan	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 16,771,888,000		$ 16,771,888,000		$ 16,142,124,000
Deferred origination fees, net			7,700,000		26,400,000
Financing receivable, accrued interest excluded from amortized costs	74,300,000		74,300,000		65,400,000
Nonaccrual loans with no allowance for credit loss	9,200,000		9,200,000		16,900,000
Number of loan modifications | loan		3		4
Number of investments with prior modification		$ 747,000		$ 760,000
Combination: Interest Rate Modification and Term Extension	$ 30,702,000		$ 31,353,000
Number of loan modifications with payment default | loan	0		0
Foreclosed assets and other real estate owned	$ 3,809,000		$ 3,809,000		2,887,000
Financing receivable, collateral dependent, amount	129,492,000		$ 129,492,000		70,926,000
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
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in process of foreclosure, amount	1,400,000		$ 1,400,000		3,000,000
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	312,000		312,000		853,000
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,245,208,000		13,245,208,000		12,581,262,000
Combination: Interest Rate Modification and Term Extension	30,617,000		30,617,000
Real Estate | OREO Received in Full or Partial Satisfaction of Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of investments with prior modification		0		0
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded commitments, allowance for credit loss	25,600,000		25,600,000		41,900,000
Reserve for unfunded commitments, expensed (released)	11,300,000	$ 16,000,000	16,300,000	$ 19,500,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,773,989,000		$ 2,773,989,000		2,837,913,000
Number of loan modifications | loan	1		1
Combination: Interest Rate Modification and Term Extension	$ 85,000		$ 736,000
Single family residential | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,657,879,000		2,657,879,000		2,546,115,000
Financing receivable, collateral dependent, amount	1,442,000		1,442,000		0
Commercial real estate | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans with subsequent default | loan				0
Paycheck Protection Program Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,600,000		5,600,000		8,900,000
Other commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	7,565,008,000		7,565,008,000		7,468,498,000
Number of loan modifications | loan		3		4
Number of investments with prior modification		$ 747,000		$ 760,000
Combination: Interest Rate Modification and Term Extension	30,617,000		30,617,000
Charge-off	9,600,000
Financing receivable, collateral dependent, amount	$ 102,384,000		$ 102,384,000		$ 65,450,000