Restructuring, Asset Impairment, and Transition Expenses - Summary of Reconciliation of Restructuring Expense by Segment (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring expense	$ 1.5	$ 1.6	$ 3.2	$ 2.3	$ 3.1	$ 5.5
2017 Altra Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	0.3	0.2	1.8	1.0	0.5	2.8
2019 Altra Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	1.2	$ 1.4	1.4	$ 1.3	2.6	2.7
Operating Segments [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	$ 1.5		$ 3.2		3.1	5.5
Operating Segments [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense					1.1	2.9
Operating Segments [Member] | Automation & Specialty [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense					2.0	2.6
Operating Segments [Member] | 2017 Altra Plan [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense					0.5	2.8
Operating Segments [Member] | 2019 Altra Plan [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense					0.6	0.1
Operating Segments [Member] | 2019 Altra Plan [Member] | Automation & Specialty [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense					$ 2.0	$ 2.6