Repurchase Agreements (Borrowings Under Repurchase Agreement And Associated Assets Pledged as Collateral) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 8,571,422	$ 7,879,087
Fair value of securities pledged as collateral under repurchase agreements	10,700,000	9,500,000
Total Fair Value of Assets Pledged and Accrued Interest	48,500	33,100
Agency MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	1,675,861	2,384,357
Fair value of securities pledged as collateral under repurchase agreements	$ 1,807,047	$ 2,572,597
Weighted average haircut (percent)	4.42%	4.60%
Non-Agency MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 1,231,908	$ 1,447,585
Fair value of securities pledged as collateral under repurchase agreements	$ 1,561,501	$ 1,871,650
Weighted average haircut (percent)	20.57%	21.38%
RPL/NPL MBS
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 642,740	$ 1,084,532
Fair value of securities pledged as collateral under repurchase agreements	$ 828,048	$ 1,377,250
Weighted average haircut (percent)	21.89%	21.31%
CRT securities
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 303,544	$ 391,586
Fair value of securities pledged as collateral under repurchase agreements	$ 377,779	$ 480,315
Weighted average haircut (percent)	19.25%	20.01%
Residential whole loans
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 3,727,526	$ 2,020,508
Fair value of securities pledged as collateral under repurchase agreements	$ 4,810,078	$ 2,441,931
Weighted average haircut (percent)	14.85%	16.55%
MSR-related assets
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 918,055	$ 474,127
Fair value of securities pledged as collateral under repurchase agreements	$ 1,164,284	$ 611,807
Weighted average haircut (percent)	21.00%	21.88%
Other Interest Earning Assets
Assets Sold under Agreements to Repurchase [Line Items]
Balance of repurchase agreements	$ 72,911	$ 76,419
Fair value of securities pledged as collateral under repurchase agreements	$ 73,925	$ 81,494
Weighted average haircut (percent)	21.20%	21.15%
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	33 days	31 days
Effective repricing period, months	10 months	8 months
Balance of repurchase agreements	$ 8,572,545	$ 7,879,114
Unamortized debt issuance expense	1,123	27
Loan Securitization
Assets Sold under Agreements to Repurchase [Line Items]
Fair value of securities pledged as collateral under repurchase agreements	238,400	27,000
Residential Loans At Fair Value
Assets Sold under Agreements to Repurchase [Line Items]
Fair Value	3,700,000	1,700,000
Amortized Cost	3,700,000	1,600,000
Total Fair Value of Assets Pledged and Accrued Interest	$ 835,800	$ 738,600