Restructuring, Asset Impairment, and Transition Expenses - Reconciliation of Accrued Restructuring Costs (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Reserve [Roll Forward]
Beginning Balance			$ 1,008,000
Restructuring expense incurred	$ 610,000	$ 680,000	2,119,000	$ 3,776,000
Cash payments			(2,503,000)
Ending Balance	624,000		624,000
2015 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance			800,000
Restructuring expense incurred	0	49,000		3,145,000
Cash payments			(532,000)
Ending Balance	268,000		268,000
2017 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance			208,000
Restructuring expense incurred	610,000	$ 631,000	2,119,000	$ 631,000
Cash payments			(1,971,000)
Ending Balance	$ 356,000		$ 356,000