Restructuring, Asset Impairment, and Transition Expenses - Reconciliation of Accrued Restructuring Costs (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 2.0	$ 1.0
Restructuring expense incurred	2.3	0.9
Cash payments	(2.0)	(0.5)
Ending Balance	2.3	1.4
2015 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance	0.4	0.8
Cash payments		(0.1)
Ending Balance	0.4	0.7
2017 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance	1.6	0.2
Restructuring expense incurred	1.0	0.9
Cash payments	(1.5)	(0.4)
Ending Balance	1.1	$ 0.7
2019 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring expense incurred	1.3
Cash payments	(0.5)
Ending Balance	$ 0.8