Fair value measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	$ 13
Derivative liabilities, fair value	$ 737	$ 1,805
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Accounts payable and other liabilities	Accounts payable and other liabilities
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
TBAs
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	$ 11	$ 1,762
Derivative liabilities, fair value	2	1,761
Futures
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	2
Derivative liabilities, fair value	735	44
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	8,700	17,050
Derivative asset, fair value	13	1,762
Derivative liabilities, fair value	737	1,805
Derivative liability, notional	6,878,700	1,914,275
Not Designated as Hedging Instrument | Other contracts | TBAs
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	3,700	1,775
Derivative asset, fair value	11	1,762
Derivative liabilities, fair value	2	1,761
Derivative liability, notional	3,700	1,775
Not Designated as Hedging Instrument | Other contracts | Forward reverse repurchase agreements
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional		15,000
Derivative asset, fair value		0
Not Designated as Hedging Instrument | Other contracts | Other
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional		275
Derivative asset, fair value		0
Not Designated as Hedging Instrument | Commodity contracts | Futures
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	5,000
Derivative asset, fair value	2
Derivative liabilities, fair value	735	44
Derivative liability, notional	$ 6,875,000	$ 1,912,500