Restructuring, Asset Impairment, and Transition Expenses - Summary of Total Restructuring Expense (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 610,000	$ 680,000	$ 2,119,000	$ 3,776,000
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	610,000	2,553,000	2,119,000	6,869,000
2015 Altra Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	49,000		3,145,000
2015 Altra Plan [Member] | Operating Segments [Member] | Couplings, Clutches and Brakes [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs				1,849,000
2015 Altra Plan [Member] | Operating Segments [Member] | Gearing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		25,000		809,000
2015 Altra Plan [Member] | Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		24,000		487,000
2017 Altra Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	610,000	631,000	2,119,000	631,000
2017 Altra Plan [Member] | Operating Segments [Member] | Couplings, Clutches and Brakes [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	609,000	$ 631,000	2,030,000	$ 631,000
2017 Altra Plan [Member] | Operating Segments [Member] | Gearing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	43,000		110,000
2017 Altra Plan [Member] | Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ (42,000)		$ (21,000)