Financing Receivable, Nonaccrual, No Allowance, Number

No definition available.

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Namespace Prefix:	slg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

+ Details

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

- Details

Name:	slg_DebtInvestmentAxis=slg_DebtInvestmentOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

Debt and Preferred Equity Investments - Rollforward of Total Allowance for Loan Loss Reserves (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023 USD ($) loan	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) loan	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Loan loss reserve activity
Balance at beginning of year			$ 6,630	$ 6,630	$ 6,630
Current period provision for loan loss	$ 0	$ 0	6,890	$ 0	0
Balance at end of period	$ 13,520		$ 13,520		$ 6,630
Number of financing receivables on non-accrual without allowance for loan loss \| loan	2		2
Debt Investment, One
Loan loss reserve activity
Financing receivable on non-accrual without allowance	$ 225,400		$ 225,400
Debt Investment, Two
Loan loss reserve activity
Financing receivable on non-accrual without allowance	$ 50,000		$ 50,000