| Cover | Apr. 29, 2021 | Mar. 04, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Apr. 29, 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 | 10020 | |
| 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 |
