Revenue Recognition - Disaggregates Revenue for Each Reportable Segment and Geographic Region (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Net sales	$ 228,483	$ 214,623	$ 706,191	$ 653,415
North America (primarily U.S.) [Member]
Disaggregation Of Revenue [Line Items]
Net sales	115,133	101,569	359,849	331,945
Europe [Member]
Disaggregation Of Revenue [Line Items]
Net sales	90,015	87,866	274,805	256,142
Asia And Other [Member]
Disaggregation Of Revenue [Line Items]
Net sales	23,335	25,188	71,537	65,328
Operating Segments [Member] | Couplings, Clutches and Brakes [Member]
Disaggregation Of Revenue [Line Items]
Net sales	118,662	110,109	361,569	327,310
Operating Segments [Member] | Electromagnetic Clutches and Brakes [Member]
Disaggregation Of Revenue [Line Items]
Net sales	57,915	58,304	192,158	187,463
Operating Segments [Member] | Gearing [Member]
Disaggregation Of Revenue [Line Items]
Net sales	54,198	48,368	159,650	144,545
Intersegment Eliminations [Member]
Disaggregation Of Revenue [Line Items]
Net sales	$ (2,292)	$ (2,158)	$ (7,186)	$ (5,903)