Goodwill and Other Intangibles Estimated Intangible Asset Amortization Expense (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Mar. 31, 2012	Mar. 31, 2011
Finite-Lived Intangible Assets [Line Items]
2013	$ 4,999
2014	3,587
2015	4,096
2016	2,109
2017	1,880
Later	12,006
Estimated intangible asset amortization expense	28,677
Customer Relationships Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
2013	1,685
2014	1,685
2015	1,685
2016	1,685
2017	1,685
Later	12,006
Estimated intangible asset amortization expense	20,431		22,116	23,801
Production and Supply Contract Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
2013	1,251
2014	1,173
2015	1,812
2016	0
2017	0
Later	0
Estimated intangible asset amortization expense	4,236		4,850	5,945
Internally Developed Software Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
2013	2,063	[1]
2014	729	[1]
2015	599	[1]
2016	424	[1]
2017	195	[1]
Later	0	[1]
Estimated intangible asset amortization expense	$ 4,010	[1]	$ 6,105	$ 8,665

[1] Estimated amortization expense for the internally developed software is based on costs accumulated as of March 31, 2013. These estimates will change as new costs are incurred and until the software is placed into service in all locations.