Derivatives - Derivative Information about U.S. Treasury Futures (Details) - USD ($)	Sep. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Derivative assets	$ 14,100,000	$ 133,000
Derivative liabilities	4,635,000	22,814,000
Margin deposit assets	328,000,000	219,000,000
Variation margin payable, derivative	4,000,000
Variation margin receivable, derivative		10,000,000
U.S. Treasury futures
Derivative [Line Items]
Derivative assets	0
Derivative liabilities	28,000,000
Fair Value		1,000,000
Interest rate swaps
Derivative [Line Items]
Derivative assets	0
Fair Value	71,000,000	153,000,000
Interest Rate Swaption
Derivative [Line Items]
Derivative liabilities	736,000
Interest Rate Swaption | Long position
Derivative [Line Items]
Derivative assets	450,000	0
Derivative assets	450,000
Derivative liabilities	736,000	0
Margin deposit assets	4,000,000
Interest Rate Swaption | Long position | Not Designated as Hedging Instrument, Economic Hedge
Derivative [Line Items]
Fair Value	11,439,000
Exchange Traded Options | Long position
Derivative [Line Items]
Derivative assets	7,500,000
Fair Value		0
Exchange Traded Options | Long position | Not Designated as Hedging Instrument, Economic Hedge
Derivative [Line Items]
Fair Value	7,500,000
TBA securities | Long position
Derivative [Line Items]
Derivative assets	6,150,000	133,000
Derivative assets	6,150,000	133,000
Derivative liabilities	3,899,000	22,814,000
Derivative liabilities	$ 3,899,000	$ 22,814,000