Restructuring And Impairment Costs (Cumulative Restructuring And Impairment Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Restructuring Cost and Reserve [Line Items]
Impairment of property, plant and equipment	$ 0	$ 0
Restructuring and impairment costs	4,113	11,661	21,504
Fiscal Year 2011 Costs [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits			11,155
Pension curtailment and settlement costs			4,081
Other restructuring costs			636
Impairment of property, plant and equipment			5,632
Restructuring and impairment costs			21,504
Fiscal Year 2011 Costs [Member] | Closure Of Processing Facility In Canada [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits			2,412
Pension curtailment and settlement costs			4,081
Other restructuring costs			0
Impairment of property, plant and equipment			5,632
Restructuring and impairment costs			12,125
Fiscal Year 2011 Costs [Member] | Other Restructuring And Cost Reduction Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits			8,743
Pension curtailment and settlement costs			0
Other restructuring costs			636
Impairment of property, plant and equipment			0
Restructuring and impairment costs			9,379
Fiscal Year 2012 Costs [Member] | Other Restructuring And Cost Reduction Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits		8,564
Pension curtailment and settlement costs		0
Other restructuring costs		3,097
Impairment of property, plant and equipment		0
Restructuring and impairment costs		11,661
Fiscal Year 2013 Costs [Member] | Other Restructuring And Cost Reduction Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	4,113
Pension curtailment and settlement costs	0
Other restructuring costs	0
Impairment of property, plant and equipment	0
Restructuring and impairment costs	4,113
Total Costs Cummulative [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	23,832
Pension curtailment and settlement costs	4,081
Other restructuring costs	3,733
Impairment of property, plant and equipment	5,632
Restructuring and impairment costs	$ 37,278