| Cover | Feb. 04, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 4, 2021 |
| Entity Registrant Name | GREENHILLÂ & CO., INC. |
| Entity File Number | 001-32147 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 51-0500737 |
| Entity Address, Address Line One | 1271 Avenue of the Americas |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10022 |
| City Area Code | 212 |
| Local Phone Number | 389-1500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | GHL |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001282977 |
