Mortgage-Backed Securities - Realized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Gross realized gains on sale of MBS	$ 4,963	$ 0	$ 5,111	$ 5,363
Gross realized losses on sale of MBS	0	(33,157)	(9,898)	(62,769)
Net unrealized gains (losses) on MBS accounted for under the fair value option	160,205	(191,752)	59,048	(215,226)
Net unrealized gains (losses) on U.S. Treasury securities	0	0	(372)	0
Net realized gains (losses) on U.S. Treasury securities	0	12	(86)	12
Total gain (loss) on investments, net	$ 165,168	$ (224,897)	$ 53,803	$ (272,620)