Income Taxes Effective Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Tax provision at statutory rate	35.00%	35.00%	35.00%
Effect of foreign operations	(1.70%)	(1.70%)	(2.10%)
Effect of foreign rate change	(3.30%)	0.00%	0.00%
State income taxes, net of federal income tax benefit	3.00%	2.80%	2.20%
Benefit of track maintenance credit	(9.10%)	(7.30%)	(21.00%)
Other, net	1.30%	0.30%	0.40%
Effective income tax rate	25.20%	29.10%	14.50%