No definition available.

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets 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
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. 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
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

+ Details

Name:	us-gaap_TradingSecuritiesDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_InterestOnlyStripMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets at Fair Value:
Agency Securities	$ 11,941,766	$ 7,051,954
Securities, trading, at fair value	883,601	939,184
Derivatives, at fair value	24,751	111,913
Liabilities at Fair Value:
Derivatives, at fair value	71,974	24,505
Fair Value, Measurements, Recurring
Assets at Fair Value:
Agency Securities	11,941,766	7,051,954
Derivatives, at fair value	24,751	111,913
Liabilities at Fair Value:
Derivatives, at fair value	71,974	24,505
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets at Fair Value:
Agency Securities	0	0
Derivatives, at fair value	0	0
Liabilities at Fair Value:
Derivatives, at fair value	0	0
Fair Value, Measurements, Recurring \| Significant Observable Inputs (Level 2)
Assets at Fair Value:
Agency Securities	11,941,766	7,051,954
Derivatives, at fair value	24,751	111,913
Liabilities at Fair Value:
Derivatives, at fair value	71,974	24,505
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 3
Assets at Fair Value:
Agency Securities	0	0
Derivatives, at fair value	0	0
Liabilities at Fair Value:
Derivatives, at fair value	0	0
Credit Risk and Non-Agency Securities
Assets at Fair Value:
Securities, trading, at fair value	883,601	819,915	$ 975,830
Credit Risk and Non-Agency Securities \| Fair Value, Measurements, Recurring
Assets at Fair Value:
Securities, trading, at fair value	883,601	819,915
Credit Risk and Non-Agency Securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets at Fair Value:
Securities, trading, at fair value	0	0
Credit Risk and Non-Agency Securities \| Fair Value, Measurements, Recurring \| Significant Observable Inputs (Level 2)
Assets at Fair Value:
Securities, trading, at fair value	883,601	819,915
Credit Risk and Non-Agency Securities \| Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 3
Assets at Fair Value:
Securities, trading, at fair value	0	0
Interest-Only Securities
Assets at Fair Value:
Securities, trading, at fair value	0	20,623	25,752
Interest-Only Securities \| Fair Value, Measurements, Recurring
Assets at Fair Value:
Securities, trading, at fair value		20,623
Interest-Only Securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets at Fair Value:
Securities, trading, at fair value		0
Interest-Only Securities \| Fair Value, Measurements, Recurring \| Significant Observable Inputs (Level 2)
Assets at Fair Value:
Securities, trading, at fair value		20,623
Interest-Only Securities \| Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 3
Assets at Fair Value:
Securities, trading, at fair value		0
U.S. Treasury Securities
Assets at Fair Value:
Securities, trading, at fair value	$ 0	98,646	$ 0
U.S. Treasury Securities \| Fair Value, Measurements, Recurring
Assets at Fair Value:
Securities, trading, at fair value		98,646
U.S. Treasury Securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets at Fair Value:
Securities, trading, at fair value		98,646
U.S. Treasury Securities \| Fair Value, Measurements, Recurring \| Significant Observable Inputs (Level 2)
Assets at Fair Value:
Securities, trading, at fair value		0
U.S. Treasury Securities \| Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 3
Assets at Fair Value:
Securities, trading, at fair value		$ 0