Loans Receivable and Other Lending Investments, net (Credit Characteristics for Performing Loans) (Details) $ in Thousands	Sep. 30, 2022 USD ($) loan	Dec. 31, 2021 USD ($) loan
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Number of non accrual loans \| loan	1	1
Commercial Portfolio Segment
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Total	$ 146,575	$ 212,683
Commercial Portfolio Segment \| Senior mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Total	133,468	199,608
Loan on non-accrual status	61,200
Commercial Portfolio Segment \| Corporate/Partnership loans
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Total		618
Commercial Portfolio Segment \| Subordinate mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
Total	13,107	$ 12,457
Commercial Portfolio Segment \| Performing Financial Instruments
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	72,309
Prior to 2018	13,107
Total	85,416
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	72,309
Prior to 2018	0
Total	72,309
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 1.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 1.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 2.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 2.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 3.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	65,559
Prior to 2018	0
Total	65,559
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 3.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	6,750
Prior to 2018	0
Total	6,750
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 4.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 4.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Senior mortgages \| Risk Rating 5.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	13,107
Total	13,107
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 1.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 1.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 2.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 2.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 3.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	13,107
Total	13,107
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 3.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 4.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 4.5
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	0
Commercial Portfolio Segment \| Performing Financial Instruments \| Subordinate mortgages \| Risk Rating 5.0
Recorded Investments in loans, presented by class and by credit quality, as indicated by risk rating
2022	0
2021	0
2020	0
2019	0
2018	0
Prior to 2018	0
Total	$ 0

Number Of Non Accrual Loans

No definition available.

Name:	star_NumberOfNonAccrualLoans
Namespace Prefix:	star_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of financing receivable originated more than five years prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447

+ Details

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

- Definition

Amount of financing receivable originated four years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in fiscal year prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

+ Details

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

- Definition

Amount of financing receivable originated three years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated two years prior to current fiscal year.

+ References

+ Details

Name:	us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

+ Details

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922355-210448

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph (a)

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingOnePointZeroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingOnePointFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingTwoPointZeroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingTwoPointFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingThreePointZeroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingThreePointFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingFourPointZeroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingFourPointFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=star_RiskRatingFivePointZeroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: