Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Effective income tax rate	25.10%
Retroactive tax benefit from extension of the short line tax credit for fiscal year 2012			$ 41,000,000
Income tax expense, other than the 2012 retroactive benefit from the Short Line Tax Credit			63,500,000
Provision for income taxes as a percentage of income from continuing operations other than 2012 retroactive benefit from the Short Line Tax Credit			26.80%
Contingent forward sale contract mark-to-market expense	0	50,106,000	0	50,106,000
Provision for income taxes	22,240,000	15,303,000	22,534,000	46,051,000
Provision for income taxes as a percentage of income from continuing operations other than non-deductible mark-to-market expense		33.40%		34.10%
Tax credits percentage of qualified maintenance expenditures to reduce federal income tax	50.00%
Tax credits limitation per mile on maintenance expenditures to reduce federal income tax	3,500
Contingent forward sale contract [Member]
Contingent forward sale contract mark-to-market expense		$ 50,100,000		$ 50,106,000