Unaudited Quarterly Results of Operations - Schedule of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Net Sales	$ 172,647		$ 173,132		$ 182,674		$ 180,453		$ 173,628		$ 183,053		$ 196,610		$ 193,361		$ 708,906	$ 746,652	$ 819,817
Gross Profit	55,127		54,175		58,200		54,630		54,204		55,800		59,986		58,473		222,132	228,463	248,869
Net income attributable to Altra Industrial Motion Corp.	$ 1,668	[1]	$ 5,313	[1]	$ 9,349	[1]	$ 8,810	[1]	$ 6,108	[1]	$ 10,221	[1]	$ 9,679	[1]	$ 9,398	[1]	$ 25,140	$ 35,406	$ 40,167
Basic net income attributable to Altra Industrial Motion Corp.	$ 0.06		$ 0.21		$ 0.36		$ 0.34		$ 0.23		$ 0.39		$ 0.37		$ 0.36		$ 0.97	$ 1.36	$ 1.50
Diluted net income attributable to Altra Industrial Motion Corp.	$ 0.06		$ 0.21		$ 0.36		$ 0.34		$ 0.23		$ 0.39		$ 0.37		$ 0.36		$ 0.97	$ 1.36	$ 1.47
Restructuring Costs	$ 3,258		$ 3,397		$ 1,641		$ 1,553		$ 2,220		$ 651		$ 2,587		$ 1,756

[1] Includes restructuring costs by quarter