Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Property, plant and equipment
Property, plant and equipment, at cost	$ 89,378	$ 87,768
Accumulated depreciation	(25,373)	(24,413)
Property, plant and equipment, net	64,005	63,355
Land [Member]
Property, plant and equipment
Property, plant and equipment, at cost	24,001	24,001
Buildings and improvements [Member]
Property, plant and equipment
Property, plant and equipment, at cost	39,963	39,613
Machinery and equipment [Member]
Property, plant and equipment
Property, plant and equipment, at cost	$ 25,414	$ 24,154