Property, Plant and Equipment (Details) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 2,100,780,000		$ 2,100,780,000		$ 2,001,019,000
Accumulated depreciation	1,515,678,000		1,515,678,000		1,469,052,000
Property, plant and equipment, net	585,102,000		585,102,000		531,967,000
Depreciation expense	24,300,000	23,000,000	47,600,000	44,400,000
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	69,895,000		69,895,000		55,624,000
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	418,525,000		418,525,000		411,149,000
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,538,405,000		1,538,405,000		1,465,255,000
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$ 73,955,000		$ 73,955,000		$ 68,991,000