Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2012

Summary of Significant Accounting Policies / Additional Balance Sheet Information [Abstract]

Revenue by segment

	Three Months Ended March 31,
	2012	2011
Minerals and materials	53%	53%
Environmental	22%	24%
Oilfield services	23%	21%
Transportation	5%	6%
Intersegment sales	-3%	-4%
	100%	100%