Represents the number of shares acquired in the equity security investment.

No definition available.

Name:	stwd_InvestmentInEquitySecuritiesNumberOfSharesAcquired
Namespace Prefix:	stwd_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage ownership in the equity security investment.

+ References

No definition available.

+ Details

Name:	stwd_InvestmentInEquitySecuritiesPercentageOwnership
Namespace Prefix:	stwd_
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:	us-gaap_InvestmentHoldingsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an unclassified balance sheet, this item represents investments in common and preferred stocks and other forms of securities that provide ownership interests in a corporation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(b))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=stwd_StarwoodEuropeanRealEstateFinanceLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investment Securities - SEREF (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2012	Dec. 31, 2016
Residential Real Estate
Ownership percentage	2.00%
SEREF
Residential Real Estate
Number of shares acquired		9,140,000
Fair value of investment	$ 13.5		$ 12.2