Secured Financing Agreements - Repurchase Agreements (Details) - Repurchase Agreements - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Secured Financing Agreements
Outstanding balance	$ 3,291,524	$ 2,476,277
Percentage of repurchase agreements for which margin calls are limited to collateral specific credit marks	72.00%
Percentage of repurchase agreements containing margin call provisions that pertain to loans held-for-sale	15.00%
Loans held for investment
Secured Financing Agreements
Outstanding balance	$ 2,692,642	1,890,925
Loans held-for-sale
Secured Financing Agreements
Outstanding balance	144,520	34,024
Investment securities.
Secured Financing Agreements
Outstanding balance	$ 454,362	$ 551,328

Represents the percentage of repurchase agreements containing margin call provisions that pertain to loans held-for-sale.

No definition available.

+ Details

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

- Definition

Represents the percentage of repurchase agreements which do not permit valuation adjustments based on capital markets activity. Margin calls on these facilities are limited to collateral-specific credit marks.

+ References

No definition available.

+ Details

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

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

- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=stwd_RepurchaseAgreementsDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis=stwd_LoanHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis=us-gaap_SecuritiesInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: