Document and Entity Information - shares shares in Millions	6 Months Ended
	Jun. 30, 2019	Jul. 31, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	Altra Industrial Motion Corp.
Entity Central Index Key	0001374535
Trading Symbol	AIMC
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-33209
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
Entity Common Stock, Shares Outstanding (in shares)		64,504,357
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock