Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 2,240,026		$ 2,240,026		$ 2,142,416
Accumulated depreciation and amortization	1,608,426		1,608,426		1,560,844
Property, plant and equipment, net	631,600		631,600		581,572
Depreciation expense	26,200	$ 24,300	50,900	$ 47,600
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	63,934		63,934		55,624
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	451,594		451,594		434,403
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,632,407		1,632,407		1,576,074
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 92,091		$ 92,091		$ 76,315