Mortgage Loans on Real Estate, Senior Financing

No definition available.

Name:	slg_MortgageLoansonRealEstateSeniorFinancing
Namespace Prefix:	slg_
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Rate of interest on investment.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

Name:	us-gaap_InvestmentInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount on the investment owned.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 20
-Section 10
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6438156&loc=d3e57880-113973

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 10
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6431724&loc=d3e32938-113948

+ Details

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

- Definition

Percentage added to reference rate used to compute variable rate on loan receivable.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansReceivableBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=slg_DebtInvestmentWithFloatingInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=slg_FixedRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateLoanTypeAxis=slg_SeniorMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateLoanTypeAxis=slg_MezzanineDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateLoanTypeAxis=slg_PreferredEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt and Preferred Equity Investments - Debt and Preferred Equity Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Carrying Value	$ 1,107,870	$ 1,088,723
Senior Financing	6,663,176
Total floating rate
Debt Instrument [Line Items]
Carrying Value	302,128
Face Value	302,903
Total fixed rate
Debt Instrument [Line Items]
Carrying Value	805,742
Face Value	815,268
Senior Mortgage Debt
Debt Instrument [Line Items]
Carrying Value	99,088
Senior Financing	$ 0
Weighted Average Yield at End of Period	4.25%
Senior Mortgage Debt \| Total floating rate
Debt Instrument [Line Items]
Carrying Value	$ 26,088
Face Value	26,233
Senior Mortgage Debt \| Total fixed rate
Debt Instrument [Line Items]
Carrying Value	73,000
Face Value	73,000
Mezzanine Debt
Debt Instrument [Line Items]
Carrying Value	726,839
Senior Financing	$ 4,700,426
Weighted Average Yield at End of Period	6.98%
Mezzanine Debt \| Total floating rate
Debt Instrument [Line Items]
Carrying Value	$ 276,040
Face Value	276,670
Mezzanine Debt \| Total fixed rate
Debt Instrument [Line Items]
Carrying Value	450,799
Face Value	459,865
Preferred Equity
Debt Instrument [Line Items]
Carrying Value	281,943
Senior Financing	$ 1,962,750
Weighted Average Yield at End of Period	9.64%
Preferred Equity \| Total floating rate
Debt Instrument [Line Items]
Carrying Value	$ 0
Face Value	0
Preferred Equity \| Total fixed rate
Debt Instrument [Line Items]
Carrying Value	281,943
Face Value	$ 282,403
Minimum \| Senior Mortgage Debt \| Total fixed rate
Debt Instrument [Line Items]
Interest rate	3.00%
Minimum \| Mezzanine Debt \| Total fixed rate
Debt Instrument [Line Items]
Interest rate	2.90%
Minimum \| Preferred Equity \| Total fixed rate
Debt Instrument [Line Items]
Interest rate	6.50%
Maximum \| Mezzanine Debt \| Total fixed rate
Debt Instrument [Line Items]
Interest rate	14.30%
Maximum \| Preferred Equity \| Total fixed rate
Debt Instrument [Line Items]
Interest rate	11.00%
LIBOR \| Minimum \| Senior Mortgage Debt \| Total floating rate
Debt Instrument [Line Items]
Basis spread on variable rate	3.50%
LIBOR \| Minimum \| Mezzanine Debt \| Total floating rate
Debt Instrument [Line Items]
Basis spread on variable rate	4.95%
LIBOR \| Maximum \| Mezzanine Debt \| Total floating rate
Debt Instrument [Line Items]
Basis spread on variable rate	12.57%