Summary of Significant Accounting Policies (Details)	Mar. 31, 2012	Mar. 31, 2011
Revenue by segment
Percentage of revenue by segment	100.00%	100.00%
Minerals and materials [Member]
Revenue by segment
Percentage of revenue by segment	53.00%	53.00%
Environmental [Member]
Revenue by segment
Percentage of revenue by segment	22.00%	24.00%
Oilfield services [Member]
Revenue by segment
Percentage of revenue by segment	23.00%	21.00%
Transportation [Member]
Revenue by segment
Percentage of revenue by segment	5.00%	6.00%
Intersegment sales [Member]
Revenue by segment
Percentage of revenue by segment	(3.00%)	(4.00%)