Disposal Group, Including Discontinued Operation, Ownership Interest Disposed

No definition available.

Name:	slg_DisposalGroupIncludingDiscontinuedOperationOwnershipInterestDisposed
Namespace Prefix:	slg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Equity Method Investment, Ownership Percentage, Deconsolidated

+ References

No definition available.

+ Details

Name:	slg_EquityMethodInvestmentOwnershipPercentageDeconsolidated
Namespace Prefix:	slg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the high end of the range of estimated fair value for investments in mortgage loans on real estate.

+ References

No definition available.

+ Details

Name:	slg_MortgageLoansOnRealEstateFairValueHighEndOfRange
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the low end of the range of estimated fair value for investments in mortgage loans on real estate.

+ References

No definition available.

+ Details

Name:	slg_MortgageLoansOnRealEstateFairValueLowEndOfRange
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number Of Impaired Retail Assets

+ References

No definition available.

+ Details

Name:	slg_NumberOfImpairedRetailAssets
Namespace Prefix:	slg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The impact of fair value adjustments on purchase price and it's impact on net income or loss for the period, gross.

+ References

No definition available.

+ Details

Name:	slg_PurchasePriceFairValueAdjustmentGross
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123351718&loc=d3e2420-110228

+ Details

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

- Definition

Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

+ Details

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

- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermDebtPercentageBearingVariableInterestAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=slg_East220Street42Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=slg_A106SpringStreetAnd133GreeneStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=slg_A106SpringStreetMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=slg_A133GreeneStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=slg_OneMadisonAvenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=slg_East220Street42Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=slg_East220Street42Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=slg_AccruedInterestPayableAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements (Details) $ in Thousands	1 Months Ended	12 Months Ended
Fair Value Measurements (Details) $ in Thousands	Dec. 31, 2020 USD ($) retailAsset	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2021
Fair Value of Financial Instruments
Marketable securities available-for-sale	$ 28,570	$ 24,146	$ 28,570
Interest rate cap and swap agreements (included in Other assets)	28	1,896	28
Purchase price and other fair value adjustment		210,070	187,522	$ 69,389
Debt and preferred equity investments	1,076,542	1,088,723	1,076,542
220 East 42nd Street
Fair Value of Financial Instruments
Ownership interest disposed					49.00%
Carrying Value
Fair Value of Financial Instruments
Fixed rate debt	3,135,572	3,274,324	3,135,572
Variable rate debt	1,827,677	801,051	1,827,677
Total	4,963,249	4,075,375	4,963,249
Fair Value
Fair Value of Financial Instruments
Marketable securities available-for-sale	28,570	24,146	28,570
Total	5,059,815	4,137,135	5,059,815
Estimated fair value of debt and preferred equity investments, low end of range	1,000,000	1,000,000	1,000,000
Estimated fair value of debt and preferred equity investments, high end of range	1,100,000	1,100,000	1,100,000
Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in Other assets)	0	0	0
Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in Other assets)	28	1,896	28
Level 3
Fair Value of Financial Instruments
Marketable securities available-for-sale	0	0	0
Interest rate cap and swap agreements (included in Other assets)	0	0	0
Level 3 \| Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments	1,076,542	1,088,723	1,076,542
Level 3 \| Fair Value
Fair Value of Financial Instruments
Fixed rate debt	3,237,075	3,336,463	3,237,075
Variable rate debt	1,822,740	800,672	1,822,740
Equity marketable securities \| Level 1
Fair Value of Financial Instruments
Marketable securities available-for-sale	0	0	0
Mortgage-backed securities
Fair Value of Financial Instruments
Marketable securities available-for-sale	28,570	24,146	28,570
Mortgage-backed securities \| Level 2
Fair Value of Financial Instruments
Marketable securities available-for-sale	$ 28,570	24,146	$ 28,570
106 Spring Street And 133 Greene Street
Fair Value of Financial Instruments
Number of impaired retail assets \| retailAsset	2
106 Spring Street
Fair Value of Financial Instruments
Asset impairment loss	$ 39,700
133 Greene Street
Fair Value of Financial Instruments
Asset impairment loss	$ 14,100
One Madison Avenue
Fair Value of Financial Instruments
Ownership percentage deconsolidated	50.50%		50.50%
Investment fair value adjustment			$ 187,500
220 East 42nd Street \| 220 East 42nd Street
Fair Value of Financial Instruments
Ownership percentage deconsolidated					51.00%
Investment fair value adjustment		206,800
Accrued Interest Payable and Other
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)	$ 61,217	29,912	61,217
Accrued Interest Payable and Other \| Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)	0	0	0
Accrued Interest Payable and Other \| Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)	61,217	29,912	61,217
Accrued Interest Payable and Other \| Level 3
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)	$ 0	$ 0	$ 0