Income Taxes (Details) AUD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015	Jun. 30, 2016 USD ($)	Jun. 30, 2015	Jun. 30, 2016 AUD	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Effective income tax rate	31.40%	35.70%	31.60%	37.60%
Tax benefit from Short Line Tax Credit	$ 7,200,000		$ 13,500,000
Tax credits percentage of qualified maintenance expenditures to reduce federal income tax			50.00%
Tax credit limitation per mile on maintenance expenditures to reduce federal income tax			$ 3,500
Non-current deferred income tax assets						$ 2,591,000	$ 2,270,000
Non-current deferred income tax liabilities						983,383,000	983,136,000
Australian Operations [Member]
Valuation allowance					AUD 2.6	$ 2,000,000
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2015-17 [Member]
Current deferred income tax assets							(69,200,000)
Non-current deferred income tax assets							200,000
Non-current deferred income tax liabilities							$ (69,000,000)