Repurchase Agreements (Borrowings Under Repurchase Agreement) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 7,278,270	$ 6,614,701
Less debt issuance costs	19	206
Amounts related to repurchase agreements not included in offsetting disclosure in Note 8	0
Repurchase Agreement Borrowings
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 7,278,289	$ 6,614,907
Weighted Average Interest Rate	3.01%	2.42%
Less debt issuance costs	$ 19	$ 206
Total repurchase agreements less debt issuance costs	7,278,270	6,614,701
Repurchase Agreement Borrowings \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 0
Weighted Average Interest Rate	0.00%
Repurchase Agreement Borrowings \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 6,011,969
Weighted Average Interest Rate	2.85%
Repurchase Agreement Borrowings \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 562,439
Weighted Average Interest Rate	3.73%
Repurchase Agreement Borrowings \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 703,881
Weighted Average Interest Rate	3.80%
Repurchase Agreement Borrowings \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 0
Weighted Average Interest Rate	0.00%
Repurchase Agreement Borrowings \| Within 30 days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 6,985,487	$ 6,161,008
Weighted Average Interest Rate	3.01%	2.39%
Repurchase Agreement Borrowings \| Over 30 days to 3 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 29,501	$ 453,899
Weighted Average Interest Rate	2.48%	2.76%
Repurchase Agreement Borrowings \| Over 3 months to 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 263,301	$ 0
Weighted Average Interest Rate	3.09%	0.00%
Agency MBS
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 2,584,097	$ 2,501,340
Agency MBS \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Agency MBS \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	2,570,990
Agency MBS \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	13,107
Agency MBS \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Agency MBS \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Legacy Non-Agency MBS
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	1,592,067	1,256,033
Legacy Non-Agency MBS \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Legacy Non-Agency MBS \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	1,544,995
Legacy Non-Agency MBS \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	47,072
Legacy Non-Agency MBS \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Legacy Non-Agency MBS \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
RPL/NPL MBS
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	913,249	567,140
RPL/NPL MBS \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
RPL/NPL MBS \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	887,087
RPL/NPL MBS \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	26,162
RPL/NPL MBS \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
RPL/NPL MBS \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
CRT securities
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	405,168	459,058
CRT securities \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
CRT securities \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	399,064
CRT securities \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	6,104
CRT securities \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
CRT securities \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
MSR related assets
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	435,762	317,255
MSR related assets \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
MSR related assets \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	342,704
MSR related assets \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	93,058
MSR related assets \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
MSR related assets \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Residential whole loans
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	1,347,946	$ 1,043,747
Residential whole loans \| Overnight
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	0
Residential whole loans \| Within 30 Days
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	267,129
Residential whole loans \| Over 30 Days to 3 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	376,936
Residential whole loans \| Over 3 Months to 12 Months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	703,881
Residential whole loans \| Over 12 months
Debt Securities, Available-for-sale [Line Items]
Balance of repurchase agreements	$ 0

Securities Sold Under Agreements To Repurchase, Net of Debt Issuance Costs

No definition available.

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- Definition

Securities Sold under Agreements to Repurchase, Amounts Not Included in Offsetting Disclosure

+ References

No definition available.

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- Definition

Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 55
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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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