Other Financial Statements Details Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 2,605,690		$ 2,605,690		$ 2,452,353
Less accumulated depreciation and amortization	1,850,910		1,850,910		1,769,015
Property, plant and equipment, net	754,780		754,780		683,338
Depreciation	32,000	$ 29,700	90,900	$ 90,300
Land
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	73,447		73,447		73,447
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	506,037		506,037		499,668
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	1,911,200		1,911,200		1,774,920
Projects in progress
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 115,006		$ 115,006		$ 104,318