Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (19,131)	$ (6,337)	$ (133,318)	$ (174,217)
Forward Contracts [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(16,891)	(522)	(45,671)	26,369
Options Held [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(3,405)	(6,226)	(22,467)	(51,259)
Interest Rate Swaption [Member] | Gain (Loss) on Interest Rate Swap and Swaption Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(12,349)	(24,394)	(62,080)	(18,397)
Total Return Swap [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(134)	(6,550)	(821)	(41,541)
Credit Default Swap, Selling Protection [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	0	(18)	0	364
Inverse Interest-Only Securities [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	1,506	1,288	2,631	22,003
Loan Purchase Commitments [Member] | Gain (Loss) on Residential Mortgage Loans Held-for-Sale [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	0	107	0	2,455
Short [Member] | Interest Rate Swap [Member] | Gain (Loss) on Interest Rate Swap and Swaption Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(5,280)	(18,381)	22,813	131,465
Long [Member] | Interest Rate Swap [Member] | Gain (Loss) on Interest Rate Swap and Swaption Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 17,422	$ 48,359	$ (27,723)	$ (245,676)