Debt - Narrative (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) class subsidiaryBusinessTrust
Debt Instrument [Line Items]
Number of classes of financial instruments | class		2
Number of business subsidiary trusts | subsidiaryBusinessTrust		2
Interest Rate Swap
Debt Instrument [Line Items]
Amount of hedged item		$ 20,000
Federal Reserve Bank Advances
Debt Instrument [Line Items]
Collateral, at carrying cost		1,200,000
Collateral, at fair value		$ 1,000,000
Proceeds from short-term debt	$ 150,000
Weighted average interest rate	4.83%
ACST III | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
ACST III | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
Junior Subordinated Debt, Preferred Securities | ACST II | London Interbank Offered Rate
Debt Instrument [Line Items]
Basis spread on variable rate		3.15%
Junior Subordinated Debt, Preferred Securities | ACST II | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate		3.15%
Federal Home Loan Bank of New York
Debt Instrument [Line Items]
Collateral, at carrying cost		$ 874,000
Collateral, at fair value		$ 741,000