| Document and Entity Information | Feb. 12, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | ALTRA INDUSTRIAL MOTION CORP. |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Central Index Key | 0001374535 |
| Document Period End Date | Feb. 12, 2021 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-33209 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 61-1478870 |
| Entity Address, Address Line One | 300 Granite Street |
| Entity Address, Address Line Two | Suite 201 |
| Entity Address, City or Town | Braintree |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02184 |
| City Area Code | 781 |
| Local Phone Number | 917-0600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of each class | Common Stock (par value $0.001) |
| Trading Symbol | AIMC |
| Name of each exchange on which registered | NASDAQ |
