Interest rate of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column B
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column B))
-URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014

+ Details

Name:	srt_MortgageLoansOnRealEstateInterestRate
Namespace Prefix:	srt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	srt_MortgageLoansOnRealEstateLineItems
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable reclassified to held for investment.

+ References

No definition available.

+ Details

Name:	stwd_FinancingReceivableReclassificationToHeldForInvestment
Namespace Prefix:	stwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The gross carrying amount of the outstanding balance due under the mortgage loan.

+ References

No definition available.

+ Details

Name:	stwd_MortgageLoansOnRealEstateGrossCarryingAmountOfMortgages
Namespace Prefix:	stwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of the contractual principal due as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	stwd_MortgageLoansOnRealEstatePrincipalAmountOfMortgages
Namespace Prefix:	stwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the weighted average duration of a group of mortgage loan receivables.

+ References

No definition available.

+ Details

Name:	stwd_MortgageLoansOnRealEstateWeightedAverageLife
Namespace Prefix:	stwd_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable reclassified to held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 11
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919244-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableReclassificationToHeldForSale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
-URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014

+ Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stwd_LoansHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stwd_LoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=stwd_InfrastructurePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_FirstMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_SecondMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=stwd_MezzanineLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=stwd_OtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=stwd_ResidentialLoansAtFairValueOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=stwd_CommercialLoansFairValueOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Held for Investment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Investments in loans
Total gross loans	$ 13,238,408	$ 12,217,352
Face Amount	13,301,495	12,262,840
Total allowance	(72,284)	(77,444)
Carrying Value	13,166,124	12,139,908	$ 11,663,870	$ 11,470,224
Total loans held-for-investment
Investments in loans
Total gross loans	12,393,777	11,164,517
Face Amount	12,461,952	11,230,344
Total allowance	(72,284)	(77,444)
Loans held-for-sale
Investments in loans
Total gross loans	844,631	1,052,835
Face Amount	839,543	1,032,496
Carrying Value	844,631	1,052,835	1,174,934	884,150
Commercial Portfolio Segment
Investments in loans
Total gross loans	10,647,450
Reclassification to held-for-sale	142,200
Loans with no related allowance	29,000
Commercial Portfolio Segment \| Total loans held-for-investment
Investments in loans
Total gross loans	10,647,450	9,653,560
Face Amount	10,695,832	9,703,608
Total allowance	(63,477)	(69,611)
Carrying Value	10,583,973	9,583,949	8,832,907	8,517,054
Infrastructure Portfolio Segment
Investments in loans
Total gross loans	1,595,615
Reclassification to held for investment	30,700
Infrastructure Portfolio Segment \| Total loans held-for-investment
Investments in loans
Total gross loans	1,595,615	1,420,273
Face Amount	$ 1,616,716	$ 1,439,940
Weighted Average Life	4 years 1 month 6 days	4 years 3 months 18 days
Total allowance	$ (8,807)	$ (7,833)
Carrying Value	$ 1,586,808	$ 1,412,440	1,381,271	1,397,448
Infrastructure Portfolio Segment \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	4.30%	4.40%
Infrastructure Portfolio Segment \| Loans held-for-sale
Investments in loans
Total gross loans	$ 89,368	$ 120,540
Face Amount	$ 89,601	$ 120,900
Weighted Average Life	2 years 7 months 6 days	3 years 2 months 12 days
Infrastructure Portfolio Segment \| Loans held-for-sale \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	2.90%	3.10%
Residential Portfolio Segment
Investments in loans
Total gross loans	$ 150,712
Weighted Average Life	28 years 10 months 24 days	27 years 10 months 24 days
Reclassification to held for investment	$ 69,500
Residential Portfolio Segment \| Total loans held-for-investment
Investments in loans
Carrying Value	150,712	$ 90,684	$ 274,758	$ 671,572
RMBS, fair value option \| Loans held-for-sale
Investments in loans
Total gross loans	444,835	841,963
Face Amount	$ 435,025	$ 820,807
RMBS, fair value option \| Loans held-for-sale \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	5.70%	6.00%
CMBS, fair value option \| Loans held-for-sale
Investments in loans
Total gross loans	$ 310,428	$ 90,332
Face Amount	$ 314,917	$ 90,789
Weighted Average Life	5 years 8 months 12 days	10 years
CMBS, fair value option \| Loans held-for-sale \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	4.30%	3.90%
First mortgage loan participation \| Total loans held-for-investment
Investments in loans
Total gross loans	$ 9,955,674
Face Amount	$ 10,003,057
Weighted Average Life	1 year 8 months 12 days
First mortgage loan participation \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	5.10%
First mortgage loan participation \| Loans held-for-sale
Investments in loans
Total gross loans		$ 8,931,772
Face Amount		$ 8,978,373
Weighted Average Life		1 year 6 months
First mortgage loan participation \| Loans held-for-sale \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)		5.30%
Subordinated mortgages \| Total loans held-for-investment
Investments in loans
Total gross loans	$ 70,457	$ 71,185
Face Amount	$ 71,428	$ 72,257
Weighted Average Life	2 years 6 months	2 years 9 months 18 days
Subordinated mortgages \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	8.80%	8.80%
Mezzanine Loans
Investments in loans
Carrying Value	$ 917,800	$ 877,300
Mezzanine Loans \| Total loans held-for-investment
Investments in loans
Total gross loans	603,119	620,319
Face Amount	$ 601,080	$ 619,352
Weighted Average Life	1 year 4 months 24 days	1 year 7 months 6 days
Mezzanine Loans \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	10.10%	10.10%
Other \| Total loans held-for-investment
Investments in loans
Total gross loans	$ 18,200	$ 30,284
Face Amount	$ 20,267	$ 33,626
Weighted Average Life	2 years 7 months 6 days	1 year 9 months 18 days
Other \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	8.20%	8.90%
Residential loans, fair value option \| Total loans held-for-investment
Investments in loans
Total gross loans	$ 150,712	$ 90,684
Face Amount	$ 149,404	$ 86,796
Residential loans, fair value option \| Total loans held-for-investment \| Weighted-average
Investments in loans
Weighted Average Coupon (as a percent)	6.20%	6.00%
Commercial loans, fair value option
Investments in loans
Total gross loans	$ 168,226