Credit Risk and Interest Rate Risk (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Secured financing agreements
Gross Amounts of Recognized  Assets (Liabilities)	$ (2,384,678)	$ (2,432,115)
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Net Amounts Offset in the Consolidated Statements of Financial Position	(2,384,678)	(2,432,115)
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Financial Instruments	3,553,582	3,539,416
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Cash Collateral (Received) Pledged	14,857	22,930
Net Amount	1,183,761	1,130,231
Derivative Asset
Net Amounts Offset in the Consolidated Statements of Financial Position	0	0
Total Repurchase Agreements and Swaptions
Gross Amounts of Recognized  Assets (Liabilities)	(2,357,873)
Gross Amounts Offset in the Consolidated Statements of Financial Position	(26,805)
Net Amounts Offset in the Consolidated Statements of Financial Position	(2,384,678)
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Financial Instruments	3,553,582
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Cash Collateral (Received) Pledged	4,859
Net Amount	1,173,763
Total Derivative Liabilities, Securities Sold and Securities Loaned
Gross Amounts of Recognized  Assets (Liabilities)		(2,413,298)
Gross Amounts Offset in the Consolidated Statements of Financial Position		(18,817)
Net Amounts Offset in the Consolidated Statements of Financial Position		(2,432,115)
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Financial Instruments		3,539,416
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Cash Collateral (Received) Pledged		11,566
Net Amount		1,118,867
Interest Rate Swaps
Derivative Asset
Gross Amounts of Recognized  Assets (Liabilities)	17,526	7,455
Gross Amounts Offset in the Consolidated Statements of Financial Position	(17,526)	(7,455)
Net Amounts Offset in the Consolidated Statements of Financial Position	0	0
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Financial Instruments	0	0
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Cash Collateral (Received) Pledged	(9,997)	(11,306)
Net Amount	(9,997)	(11,306)
Swaptions
Derivative Asset
Gross Amounts of Recognized  Assets (Liabilities)	9,279	11,362
Gross Amounts Offset in the Consolidated Statements of Financial Position	(9,279)	(11,362)
Net Amounts Offset in the Consolidated Statements of Financial Position	0	0
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Financial Instruments	0	0
Gross Amounts Not Offset with Financial Assets (Liabilities) in the Consolidated Statements of Financial Position, Cash Collateral (Received) Pledged	(1)	(58)
Net Amount	$ (1)	$ (58)