Business Acquisition (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2012	Oct. 16, 2012	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2011
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs	$ 3,205
Business Acquisition, Cost of Acquired Entity, Purchase Price	270,000	110,000
Cash and Cash Equivalents, at Carrying Value	156,609		150,821	134,111	193,016
Accounts Receivable, Net, Current	231,034		280,324
Inventory, Net	160,537		157,712
Property, Plant and Equipment, Net	413,763		386,409
Assets	1,632,732		1,405,696
Accounts Payable, Current	70,575		83,188
Other Liabilities	5,022		5,217
Liabilities	751,106		583,032
Business Acquisition, Purchase Price Allocation, Property, Plant and Equipment	7,000
Cash [Member]
Business Acquisition [Line Items]
Cash and Cash Equivalents, at Carrying Value	767
Inventories [Member]
Business Acquisition [Line Items]
Accounts Receivable, Net, Current	8,291
Inventories [Member]
Business Acquisition [Line Items]
Inventory, Net	7,228
Property, Plant and Equipment, Type [Domain]
Business Acquisition [Line Items]
Property, Plant and Equipment, Net	12,457
Other Assets [Member]
Business Acquisition [Line Items]
Other Assets	913
Finite-Lived Intangible Assets, Major Class Name [Domain]
Business Acquisition [Line Items]
Intangible Assets, Net (Excluding Goodwill)	144,000
goodwill acquired or allocated member [Member]
Business Acquisition [Line Items]
Goodwill	109,116
Assets, Total [Member]
Business Acquisition [Line Items]
Assets	282,772
Accounts Payable [Member]
Business Acquisition [Line Items]
Accounts Payable, Current	(2,167)
Other Liabilities [Member]
Business Acquisition [Line Items]
Other Liabilities	(3,243)
Liabilities, Total [Member]
Business Acquisition [Line Items]
Liabilities	(5,410)
net assets acquired [Member]
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	$ 277,362