Restructuring, Asset Impairment, and Transition Expenses - Reconciliation of Accrued Restructuring Costs (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Beginning Balance			$ 1,008,000
Restructuring expense incurred	$ 566,000	$ 1,198,000	1,509,000	$ 3,096,000
Cash payments			(1,637,000)
Ending Balance	880,000		880,000
2015 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance			800,000
Restructuring expense incurred	0	$ 1,198,000		$ 3,096,000
Cash payments			(296,000)
Ending Balance	504,000		504,000
2017 Altra Plan [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance			208,000
Restructuring expense incurred	566,000		1,509,000
Cash payments			(1,341,000)
Ending Balance	$ 376,000		$ 376,000