Contingencies and Legacy Environmental Commitments - Schedule of Environmental Activity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013
Environmental Remediation Obligations [Abstract]
Environmental activity, Beginning balance	$ 12,684
Environmental costs incurred	(324)	(239)	(1,245)
Interest accretion	90
Reduction of environmental reserve-Wyoming Illinois	(1,207)
Environmental activity, Ending balance	$ 11,243		$ 12,684

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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