Loans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Purchased with Credit Deterioration, Discount (Premium)	$ 9,000		$ 9,600
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available	5,400,000		4,800,000
Proceeds from sale of SBA loans	23,100	$ 8,800
Gain on sale of SBA loans	1,394	501
Consumer mortgage loans secured by residential real estate in process of foreclosure	0		1,000
Allowance for credit loss adjustment	40,300
Nonperforming loan balances, excluding government guaranteed balances	9,600		10,700
Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Default subsequent to term extension	2,752	0
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	71,200		66,700
Enterprise Value Lending Portfolio Niche Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit loss adjustment	14,400
Commercial and industrial | Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Default subsequent to term extension	1,000
Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	135,498	138,295	134,771	$ 136,932
Non-Covered Loans | Enterprise Value Lending Portfolio Niche Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	22,700		23,000
Non-Covered Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	58,714	$ 59,149	$ 58,886	$ 53,835
Cumulative Effect, Period Of Adoption, Adjustment | Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, allowance for credit loss	$ 12,800