Fair Value of Financial Instruments (Carry Value vs Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	$ 6,509,333	$ 7,023,050
MSR related assets	611,807	492,080
Residential whole loans, at carrying value	3,016,715	908,516
Residential whole loans, at fair value	1,665,978	1,325,115
Securities obtained and pledged as collateral	0	504,062
Restricted cash	36,744	13,986
Repurchase agreements	7,879,087	6,614,701
Securitized debt	684,420	363,944
Obligation to return securities held as collateral, at fair value	0	504,062
Senior Notes	96,816	96,773
Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
MSR related assets	611,807	492,080
Securities obtained and pledged as collateral	0	504,062
Cash and cash equivalents	51,965	449,757
Restricted cash	36,744	13,986
Repurchase agreements	7,879,087	6,614,701
Securitized debt	684,420	363,944
Obligation to return securities held as collateral, at fair value	0	504,062
Senior Notes	96,816	96,773
Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
MSR related assets	611,807	493,026
Securities obtained and pledged as collateral	0	504,062
Cash and cash equivalents	51,965	449,757
Restricted cash	36,744	13,986
Repurchase agreements	7,896,672	6,623,255
Securitized debt	680,209	366,109
Obligation to return securities held as collateral, at fair value	0	504,062
Senior Notes	99,951	103,729
Agency MBS
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,698,213	2,824,681
Repurchase agreements	2,384,357	2,501,340
Agency MBS \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,698,213	2,824,681
Agency MBS \| Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,698,213	2,824,681
Non-Agency MBS
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	3,318,299	3,533,966
Repurchase agreements	1,447,585	1,256,033
Non-Agency MBS \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	3,318,299	3,533,966
Non-Agency MBS \| Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	3,318,299	3,533,966
CRT securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	492,821	664,403
Repurchase agreements	391,586	459,058
CRT securities \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	492,821	664,403
CRT securities \| Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	492,821	664,403
Residential whole loans, at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential whole loans, at fair value	1,665,978	1,325,115
Repurchase agreements	2,020,508	1,043,747
Residential whole loans, at fair value \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential whole loans, at carrying value	3,016,715	908,516
Residential whole loans, at fair value	1,665,978	1,325,115
Residential whole loans, at fair value \| Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential whole loans, at carrying value	3,104,401	988,688
Residential whole loans, at fair value	$ 1,665,978	$ 1,325,115

Residential Whole Loans, Carrying Value

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value at acquisition of acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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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.

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The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

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Secured financing other than securities sold under agreements to repurchase and securities loaned.

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

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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.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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