Offsetting assets and liabilities - Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Effect of offsetting recognized liabilities, Derivative
Gross Amounts of Recognized Liabilities	$ 212	$ 1,319
Effect of offsetting recognized liabilities, Total
Gross Amounts of Recognized Liabilities, Total	2,138,323	2,866,065
Liabilities Presented in the Consolidated Balance Sheets, Total	2,138,323	2,866,065
Financial Instruments, Total	2,136,671	2,850,720
Net Amount, Total	1,652	15,345
TBA agency securities
Effect of offsetting recognized liabilities, Derivative
Gross Amounts of Recognized Liabilities	212	1,319
Liabilities Presented in the Consolidated Balance Sheets, Derivative	212	1,319
Cash Collateral Paid, Derivative		1,319
Net Amount, Derivative	212
Secured borrowings
Effect of offsetting recognized liabilities, Borrowings
Gross Amounts of Recognized Liabilities, Borrowings	2,102,075	2,663,735
Liabilities Presented in the Consolidated Balance Sheets, Borrowings	2,102,075	2,663,735
Financial Instruments, Borrowings	2,102,075	2,663,735
Paycheck Protection Program Liquidity Facility
Effect of offsetting recognized liabilities, Borrowings
Gross Amounts of Recognized Liabilities, Borrowings	36,036	201,011
Liabilities Presented in the Consolidated Balance Sheets, Borrowings	36,036	201,011
Financial Instruments, Borrowings	34,596	186,985
Net Amount, Borrowings	$ 1,440	$ 14,026