Loans - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) loan	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) loan	Dec. 31, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Purchased with Credit Deterioration, Discount (Premium)			$ 9,100,000		$ 11,900,000
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available	$ 3,900,000,000		3,900,000,000		2,800,000,000
Proceeds from sale of SBA loans	33,300,000	$ 0	42,100,000	$ 0
Gain on sale of SBA loans	1,500,000		2,015,000	0
Consumer mortgage loans secured by residential real estate in process of foreclosure	1,000,000		1,000,000		0
Allowance for credit loss adjustment	39,300,000		39,300,000
Nonperforming loan balances, excluding government guaranteed balances	6,000,000		6,000,000		6,700,000
Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Default subsequent to term extension			0
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	64,500,000		64,500,000		48,100,000
Enterprise Value Lending Portfolio Niche Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit loss adjustment	13,800,000		13,800,000
Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	142,133,000	140,572,000	142,133,000	140,572,000	136,932,000	$ 141,319,000	$ 140,546,000	$ 145,041,000
Interest income on nonaccrual loans	0	$ 0	0	$ 0
Number of loans restructured | loan		0		0
Number of troubled debt restructuring subsequently defaulted | loan		0		0
Non-Covered Loans | Enterprise Value Lending Portfolio Niche Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	21,700,000		21,700,000
Non-Covered Loans | Agriculture Portfolio Niche Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss					16,100,000
Non-Covered Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	62,476,000	$ 69,168,000	62,476,000	$ 69,168,000	$ 53,835,000	$ 60,318,000	$ 65,646,000	$ 63,825,000
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	$ 12,900,000		$ 12,900,000