Restructuring, Asset Impairment, and Transition Expenses - Summary of Reconciliation of Restructuring Expense by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring expense	$ 1.6	$ 2.3
2017 Altra Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	0.2	1.0
2019 Altra Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	1.4	1.3
Operating Segments [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	1.6	$ 2.3
Operating Segments [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	0.6
Operating Segments [Member] | Automation & Specialty [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	1.0
Operating Segments [Member] | 2017 Altra Plan [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	0.2
Operating Segments [Member] | 2019 Altra Plan [Member] | Power Transmission Technologies [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	0.4
Operating Segments [Member] | 2019 Altra Plan [Member] | Automation & Specialty [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense	$ 1.0