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Residential Mortgage Securities and MSR-Related Assets (Impact of AFS Securities on AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI from AFS Securities:
Unrealized gain on AFS securities at beginning of period	$ 392,722	$ 417,167
Unrealized (loss)/gain on AFS securities, net	124,410	22,103
Reclassification adjustment for MBS sales included in net income	(23,953)	(17,009)
Reclassification adjustment for impairment included in net income	(344,269)	0
Change in AOCI from AFS securities	(243,812)	5,094
Balance at end of period	148,910	422,261
Agency MBS
AOCI from AFS Securities:
Unrealized (loss)/gain on AFS securities, net	4,876	9,315
Non-Agency MBS
AOCI from AFS Securities:
Unrealized (loss)/gain on AFS securities, net	124,700	12,276
MSR-related assets
AOCI from AFS Securities:
Unrealized (loss)/gain on AFS securities, net	$ (5,166)	$ 512

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Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment Excluding Cumulative Effect, Net of Tax, Portion Attributable to Parent

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