Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, collectively evaluated for impairment		$ 8,243,143		$ 8,253,253
Financing receivable, allowance for credit losses, collectively evaluated for impairment		74,507		74,882
Financing receivable, individually evaluated for impairment and acquired with deteriorated credit quality		77,300
Financing receivable, allowance for credit losses, individually evaluated for impairment and acquired with deteriorated credit quality		2,300
Loans, individually evaluated for impairment		8,586		20,789
Allowance for credit loss, available for sale	$ 160	0	$ 160	0	$ 310
Allowance for credit loss, held to maturity	157	146	157	146	$ 107
Charge-offs		0	(6,640)
(Benefit) provision for credit loss expense		(2,860)	6,490
Debt securities, accrued interest after allowance for credit loss		8,200		8,100
Off-balance sheet, credit loss, liability		2,400		$ 2,500
Off-balance sheet, credit loss, liability, credit loss expense (reversal)		(72)	140
Signature Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Charge-offs	(6,600)		(6,600)
(Benefit) provision for credit loss expense	$ 6,600		$ 6,600
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment and acquired with deteriorated credit quality		2,300
Loans, individually evaluated for impairment		$ 68,700