Name:	slg_DeferredCompensationArrangementWithIndividualMaximumPercentageOfTheCompensationThatMayBeDeferred
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the low end of the range of annual vesting rates that occurs once performance criteria are reached.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRateHighEndOfRange
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the low end of the range of annual vesting rates that occurs once performance criteria are reached.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRateLowEndOfRange
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the duration of each offering period during which the shares are offered for purchase under the stock-based compensation plan of the entity.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardDurationOfOfferingPeriods
Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the weighted average fair value of awards granted during the period.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardGrantsInPeriodFairValue
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the number of shares that would be issued under the plan if shares issued is equal to fungible units; actual shares issued may be more or less depending on the type of awards issued and the ratio of fungible units to shares under each award.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesToBeIssuedIfEqualToFungibleUnits
Namespace Prefix:	slg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Represents the period from the date of grant of the awards for the commencement of vesting of awards.

No definition available.

Name:	slg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPeriodOfAwardVestingCommencement
Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Share Based Compensation Arrangement by Share Based Payment Award, Fungible Units Per Share

No definition available.

Name:	slg_ShareBasedCompensationArrangementbyShareBasedPaymentAwardFungibleUnitsPerShare
Namespace Prefix:	slg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Represents the maximum number of fungible units authorized to be granted by the entity.

No definition available.

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

Share Based Compensation Arrangement by Share Based Payment Award, Preferred Unit Distributions as a Percentage of Common Unit Distributions

No definition available.

Name:	slg_ShareBasedCompensationArrangementbyShareBasedPaymentAwardPreferredUnitDistributionsasaPercentageofCommonUnitDistributions
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Share-based Compensation Arrangement By Share-based Payment Award, Number Of Fungible Units Available For Grant

No definition available.

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

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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

Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 25
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=109244457&loc=d3e16701-113920

Name:	us-gaap_CommonStockSharesHeldInEmployeeTrustShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Amount of cost capitalized for award under share-based payment arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Discount rate from fair value on offering date that participants pay for shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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

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.

No definition available.

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

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Net number of share options (or share units) granted during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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

Name:	us-gaap_AwardTypeAxis=slg_ClassOLTIPUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_AwardTypeAxis=slg_RestrictedStockAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_AwardTypeAxis=slg_LongTermIncentivePlanUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=slg_ThirdAmendmentandRestated2005StockOptionandIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=slg_StockOptionsStockAppreciationRightsAndOtherAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=slg_OtherAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PlanNameAxis=slg_DeferredStockCompensationPlanForDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: