Name:	slg_IncrementalCommonSharesAttributableToRedemptionOfUnitsToCommonShares
Namespace Prefix:	slg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic

No definition available.

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

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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

No definition available.

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

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of dilutive convertible securities excluding adjustments related to ESOP convertible preferred stock, stock options, and restrictive stock units.

No definition available.

Name:	us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 66
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e2814-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780133-109256

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e2740-109256

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60A
-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780132-109256

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

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 28A
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1500-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1377-109256

Name:	us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

No definition available.

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

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1505-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1377-109256

Name:	us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

No definition available.

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

Amount of undistributed earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780133-109256

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

No definition available.

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

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1505-109256

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

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1448-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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

No definition available.