Property, Plant and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 1,942,994,000		$ 1,942,994,000		$ 1,897,685,000
Accumulated depreciation	1,424,803,000		1,424,803,000		1,383,141,000
Property, plant and equipment, net	518,191,000		518,191,000		514,544,000
Depreciation expense	23,000,000	22,400,000	44,400,000	43,100,000
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	55,464,000		55,464,000		47,102,000
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	395,971,000		395,971,000		396,611,000
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,421,806,000		1,421,806,000		1,377,814,000
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 69,753,000		$ 69,753,000		$ 76,158,000