Revenue Recognition - Disaggregates Revenue for Each Reportable Segment and Geographic Region (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Net sales	$ 237,323	$ 223,357	$ 477,708	$ 438,792
North America (primarily U.S.) [Member]
Disaggregation Of Revenue [Line Items]
Net sales	119,023	115,236	244,716	230,376
Europe [Member]
Disaggregation Of Revenue [Line Items]
Net sales	91,308	84,983	184,790	168,275
Asia And Other [Member]
Disaggregation Of Revenue [Line Items]
Net sales	26,992	23,138	48,202	40,141
Operating Segments [Member] | Couplings, Clutches and Brakes [Member]
Disaggregation Of Revenue [Line Items]
Net sales	122,734	110,969	242,907	217,201
Operating Segments [Member] | Electromagnetic Clutches and Brakes [Member]
Disaggregation Of Revenue [Line Items]
Net sales	65,136	65,281	134,243	129,159
Operating Segments [Member] | Gearing [Member]
Disaggregation Of Revenue [Line Items]
Net sales	51,567	49,149	105,452	96,177
Intersegment Eliminations [Member]
Disaggregation Of Revenue [Line Items]
Net sales	$ (2,114)	$ (2,042)	$ (4,894)	$ (3,745)