Nature of Operations and Summary of Significant Accounting Policies Cash equivalents and supplemental cash flow information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Property, Plant and Equipment [Line Items]
Interest Expense	$ 12,496	$ 12,496	$ 13,360
Income Tax Expense (Benefit)	52,213	64,372	61,988
Proceeds from Income Tax Refunds	$ 408	$ 3,067	$ 4,864
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3-35
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3-40
Building [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	2-50
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	20