Supplemental Balance Sheets and Statements of Operations - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,271,930	$ 1,030,587
Accumulated depreciation	(866,614)	(821,276)
Property, plant and equipment	405,316	209,311
Land and land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	66,150	21,642
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	186,207	140,895
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	895,914	783,288
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	72,811	68,706
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	46,391	14,653
Other Capitalized Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 4,457	$ 1,403