Income Taxes (Details 3)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Tax provision at statutory rate	35.00%	35.00%	35.00%
Effect of acquisitions/divestitures	(3.10%)	0.00%	0.00%
Effect of foreign operations	(2.90%)	(1.20%)	(2.60%)
State income taxes, net of federal income tax benefit	2.30%	3.10%	4.20%
Benefit of track maintenance credit	(6.50%)	(9.30%)	(15.00%)
Other, net	(0.40%)	0.10%	(0.70%)
Effective income tax rate	24.40%	27.70%	20.90%