Cover Page - shares	6 Months Ended
	Jun. 30, 2019	Aug. 06, 2019
Document Information [Line Items]
Entity Interactive Data Current	Yes
Local Phone Number	594-2700
City Area Code	212
Entity Address, Postal Zip Code	10170
Entity Address, State or Province	NY
Entity Address, City or Town	New York
Entity Address, Address Line One	420 Lexington Avenue
Entity Tax Identification Number	13-3956755
Entity Incorporation, State or Country Code	MD
Entity File Number	1-13199
Document Transition Report	false
Document Quarterly Report	true
Entity Registrant Name	SL GREEN REALTY CORP
Entity Central Index Key	0001040971
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Emerging Growth Company	false
Entity Small Business	false
Amendment Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		82,416,822
Entity Current Reporting Status	Yes
SL Green Operating Partnership [Member]
Document Information [Line Items]
Entity Interactive Data Current	Yes
Entity Tax Identification Number	13-3960938
Entity Incorporation, State or Country Code	DE
Entity File Number	33-167793-02
Entity Registrant Name	SL GREEN OPERATING PARTNERSHIP, L.P.
Entity Central Index Key	0001492869
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Emerging Growth Company	false
Entity Small Business	false
Amendment Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,022,624
Entity Current Reporting Status	Yes
Preferred Stock
Document Information [Line Items]
Security Exchange Name	NYSE
Title of 12(b) Security	6.500% Series I Cumulative Redeemable Preferred Stock, $0.01 par value
Trading Symbol	SLG.PRI
Common Stock
Document Information [Line Items]
Security Exchange Name	NYSE
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	SLG