Segments, Concentrations and Geographic Information - Reconciliation of Segment Assets to Consolidated Assets (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total depreciation and amortization		$ 9,276	$ 8,809	$ 18,679	$ 17,615
Total assets		906,552	911,087	906,552	911,087	$ 920,657
Corporate [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total depreciation and amortization		869	824	1,739	1,628
Total assets	[1]	22,553	29,893	22,553	29,893
Couplings, Clutches and Brakes [Member] | Operating Segments [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total depreciation and amortization		5,505	5,133	11,230	10,270
Total assets		565,603	557,642	565,603	557,642
Electromagnetic Clutches and Brakes [Member] | Operating Segments [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total depreciation and amortization		1,005	1,201	1,935	2,416
Total assets		158,325	185,839	158,325	185,839
Gearing [Member] | Operating Segments [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total depreciation and amortization		1,897	1,651	3,775	3,301
Total assets		$ 160,071	$ 137,713	$ 160,071	$ 137,713

[1] Corporate assets are primarily cash and cash equivalents, tax related asset accounts, certain capitalized software costs, property, plant and equipment and deferred financing costs.