Repurchase Agreements (Borrowings Under Repurchase Agreement And Associated Assets Pledged as Collateral)(Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 5,892,228	$ 6,614,701
Unamortized debt issuance expense	53	206
Agency MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	2,111,547	2,501,340
Fair value of securities pledged as collateral under repurchase agreements	$ 2,283,312	$ 2,705,754
Weighted average haircut (percent)	4.52%	4.65%
Non-Agency MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 1,364,458	$ 1,256,033
Fair value of securities pledged as collateral under repurchase agreements	$ 1,813,359	$ 1,652,983
Weighted average haircut (percent)	21.24%	21.87%
RPL/NPL MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 499,294	$ 567,140
Fair value of securities pledged as collateral under repurchase agreements	$ 634,073	$ 726,540
Weighted average haircut (percent)	22.01%	22.05%
U.S. Treasury securities
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 220,931	$ 470,334
Fair value of securities pledged as collateral under repurchase agreements	$ 220,731	$ 472,095
Weighted average haircut (percent)	1.00%	1.47%
CRT securities
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 410,157	$ 459,058
Fair value of securities pledged as collateral under repurchase agreements	$ 516,486	$ 595,900
Weighted average haircut (percent)	20.43%	22.16%
MSR related assets
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 297,063	$ 317,255
Fair value of securities pledged as collateral under repurchase agreements	$ 381,390	$ 482,158
Weighted average haircut (percent)	21.70%	33.19%
Residential whole loans
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 988,831	$ 1,043,747
Fair value of securities pledged as collateral under repurchase agreements	$ 1,382,068	$ 1,474,704
Weighted average haircut (percent)	25.55%	26.10%
Repurchase Agreement Borrowings
Assets Sold under Agreements to Repurchase [Line Items]
Weighted average remaining term-to-interest rate reset of borrowings under repurchase agreements, days	14 days	16 days
Effective repricing period, months	9 months	11 months
Balance of repurchase agreements	$ 5,892,281	$ 6,614,907
Unamortized debt issuance expense	$ 53	$ 206