| Cover | Jan. 21, 2022 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 21, 2022 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 1-13199 |
| Entity Registrant Name | SL GREEN REALTY CORP. |
| Entity Central Index Key | 0001040971 |
| Entity Tax Identification Number | 13-3956775 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | One Vanderbilt Avenue |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10017 |
| City Area Code | 212 |
| Local Phone Number | 594-2700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | SLG |
| Security Exchange Name | NYSE |
| Preferred Stock | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 6.500% Series I Cumulative Redeemable Preferred Stock, $0.01 par value |
| Trading Symbol | SLG.PRI |
| Security Exchange Name | NYSE |
