| Document And Entity Information | Feb. 28, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 28, 2023 |
| Entity Registrant Name | Montrose Environmental Group, Inc. |
| Entity Central Index Key | 0001643615 |
| Entity Emerging Growth Company | false |
| Securities Act File Number | 001-39394 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 46-4195044 |
| Entity Address, Address Line One | 5120 Northshore Drive |
| Entity Address, City or Town | North Little Rock |
| Entity Address, State or Province | AR |
| Entity Address, Postal Zip Code | 72118 |
| City Area Code | 501 |
| Local Phone Number | 900-6400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.000004 par value per share |
| Trading Symbol | MEG |
| Security Exchange Name | NYSE |
