Number of securities.

No definition available.

Name:	stwd_NumberOfSecurities
Namespace Prefix:	stwd_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percent Of Outstanding Loan Earning Fixed-Rate Weighted Average Interest

+ References

No definition available.

+ Details

Name:	stwd_PercentOfOutstandingLoanEarningFixedRateWeightedAverageInterest
Namespace Prefix:	stwd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The value of the collateral (typically cash) that the entity receives in a financing transaction in exchange for securities lent. This item represents a liability in the financial statements of the lender of the securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 25
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109249708&loc=d3e113275-111724

Reference 2: 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))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_CollateralAxis=us-gaap_CollateralPledgedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CollateralAxis=us-gaap_FinanceReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=stwd_CollateralizedLoanObligationsSTWD2019FL1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=stwd_CollateralizedLoanObligationsSTWD2021FL2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=stwd_CollateralizedLoanObligationsSTWD2021SIF1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=stwd_CollateralizedLoanObligationsSTWD2021HTSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Secured Borrowings - Collateralized Loan Obligations (Details) $ in Thousands	1 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2021	Sep. 30, 2021 USD ($) Item	Dec. 31, 2020 USD ($) Item	May 31, 2021 USD ($)	Apr. 30, 2021 USD ($)	Aug. 31, 2019 USD ($)
Summary of CLO
Carrying value		$ 2,614,230	$ 930,554
Collateral assets
Summary of CLO
Amount issued		3,028,170
Carrying value		3,123,658
Financing
Summary of CLO
Amount issued		2,633,841
Carrying value		$ 2,614,230
LIBOR
Summary of CLO
Spread	2.22%
STWD 2019-FL1
Summary of CLO
Amount issued						$ 1,100,000
STWD 2019-FL1 \| Collateral assets
Summary of CLO
Count \| Item		25	23
Amount issued		$ 1,034,361	$ 1,002,445
Carrying value		$ 1,103,259	$ 1,099,439
STWD 2019-FL1 \| Financing
Summary of CLO
Count \| Item		1	1
Amount issued		$ 936,375	$ 936,375
Carrying value		$ 932,425	$ 930,554
STWD 2019-FL1 \| LIBOR \| Collateral assets
Summary of CLO
Spread		4.23%	3.93%
STWD 2019-FL1 \| LIBOR \| Financing
Summary of CLO
Spread			1.64%
STWD 2019-FL1 \| SOFR \| Financing
Summary of CLO
Spread		1.63%
STWD 2021-FL2
Summary of CLO
Amount issued				$ 1,300,000
Percent of outstanding loan		7.00%
Debt, weighted average interest rate		7.55%
STWD 2021-FL2 \| Collateral assets
Summary of CLO
Count \| Item		25
Amount issued		$ 1,269,744
Carrying value		$ 1,279,245
STWD 2021-FL2 \| Financing
Summary of CLO
Count \| Item		1
Amount issued		$ 1,077,375
Carrying value		$ 1,069,014
STWD 2021-FL2 \| LIBOR \| Collateral assets
Summary of CLO
Spread		4.23%
STWD 2021-FL2 \| LIBOR \| Financing
Summary of CLO
Spread		1.78%
STWD 2021-SIF1
Summary of CLO
Amount issued					$ 500,000
Percent of outstanding loan		2.00%
Debt, weighted average interest rate		5.62%
STWD 2021-SIF1 \| Collateral assets
Summary of CLO
Count \| Item		31
Amount issued		$ 494,065
Carrying value		$ 510,592
STWD 2021-SIF1 \| Financing
Summary of CLO
Count \| Item		1
Amount issued		$ 410,000
Carrying value		$ 404,960
STWD 2021-SIF1 \| LIBOR \| Collateral assets
Summary of CLO
Spread		3.94%
STWD 2021-SIF1 \| LIBOR \| Financing
Summary of CLO
Spread		2.15%
STWD 2021-HTS \| Collateral assets
Summary of CLO
Count \| Item		1
Amount issued		$ 230,000
Carrying value		$ 230,562
STWD 2021-HTS \| Financing
Summary of CLO
Count \| Item		1
Amount issued		$ 210,091
Carrying value		$ 207,831
STWD 2021-HTS \| LIBOR \| Collateral assets
Summary of CLO
Spread		4.34%
STWD 2021-HTS \| LIBOR \| Financing
Summary of CLO
Spread		2.47%