Noncontrolling Interest, Accrued Dividends On Preferred Units

No definition available.

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

- Definition

Rollforward Analysis of Preferred Unit Activity [Roll Forward]

+ References

No definition available.

+ Details

Name:	slg_RollforwardAnalysisofPreferredUnitActivityRollForward
Namespace Prefix:	slg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569655-111683

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4616395-111683

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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

- Definition

Carrying amount of the equity interests owned by noncontrolling preferred unit holders in an entity included in the reporting entity's consolidated financial statements.

+ References

No definition available.

+ Details

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

- Definition

Amount of increase in noncontrolling interest from subsidiary issuance of equity interests to noncontrolling interest holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569655-111683

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_PreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Unit Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ 0	$ (54)	$ (1,536)	$ (25,791)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	0	$ (54)	(1,536)	(25,791)
SL Green Operating Partnership \| Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period			$ 283,285	$ 300,427	$ 283,285	$ 300,427
Issuance of preferred units					0	1,000
Redemption of preferred units					(82,750)	(18,142)
Accrued dividends on preferred units					1,634	0
Balance at end of period	$ 202,169				$ 202,169	$ 283,285