Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 2,177,949		$ 2,142,416
Accumulated depreciation and amortization	1,582,702		1,560,844
Property, plant and equipment, net	595,247		581,572
Depreciation expense	24,700	$ 23,300
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	55,624		55,624
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	437,751		434,403
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,598,481		1,576,074
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 86,093		$ 76,315