Loans - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024 USD ($) loan	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Purchased with Credit Deterioration, Discount (Premium)	$ 8,500,000				$ 9,600,000
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available	5,500,000,000		$ 5,500,000,000		4,800,000,000
Proceeds from sale of SBA loans	23,100,000	$ 33,300,000	1,400,000	$ 42,100,000
Gain on sale of SBA loans		1,500,000	1,415,000	2,015,000
Consumer mortgage loans secured by residential real estate in process of foreclosure	0		0		1,000,000.0
Financing receivable, allowance for credit loss	139,778,000		139,778,000		134,771,000
Allowance for credit loss adjustment	49,100,000		49,100,000
Nonperforming loan balances, excluding government guaranteed balances	$ 11,900,000		11,900,000		10,700,000
Number of loans that experienced default | loan	0
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 52,500,000		52,500,000		66,700,000
Enterprise Value Lending Portfolio Niche Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit loss adjustment	16,100,000		16,100,000
Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of SBA loans	0
Financing receivable, allowance for credit loss	139,778,000	142,133,000	139,778,000	142,133,000	134,771,000	$ 139,464,000	$ 141,319,000	$ 136,932,000
Non-Covered Loans | Enterprise Value Lending Portfolio Niche Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	23,000,000.0		23,000,000.0
Non-Covered Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	64,060,000	$ 62,476,000	64,060,000	$ 62,476,000	$ 58,886,000	$ 61,478,000	$ 60,318,000	$ 53,835,000
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	$ 14,500,000		$ 14,500,000
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans | Baseline
Accounts, Notes, Loans and Financing Receivable [Line Items]
Growth upside forecast	0.40		0.40
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans | Near-term growth upside
Accounts, Notes, Loans and Financing Receivable [Line Items]
Growth upside forecast	0.30		0.30
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans | Moderate recession downside
Accounts, Notes, Loans and Financing Receivable [Line Items]
Growth upside forecast	0.30		0.30