| Document and Entity Information | Dec. 07, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | MOELIS & CO |
| Security Exchange Name | NYSE |
| Entity Address, State or Province | NY |
| Amendment Flag | false |
| Entity Central Index Key | 0001596967 |
| Document Type | 8-K |
| Document Period End Date | Dec. 7, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36418 |
| Entity Tax Identification Number | 46-4500216 |
| Entity Address, Address Line One | 399 Park Avenue |
| Entity Address, Address Line Two | 5th Floor |
| Entity Address, City Or Town | New York |
| Entity Address, Postal Zip Code | 10022 |
| City Area Code | (212) |
| Local Phone Number | 883-3800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre commencement Tender Offer | false |
| Pre commencement Issuer Tender Offer | false |
| Security 12b Title | Class A Common Stock |
| Trading Symbol | MC |
| Entity Emerging Growth Company | false |
