Income Taxes (Details) AUD in Millions	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015	Mar. 31, 2016 AUD	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Effective income tax rate	32.20%	41.40%
Tax benefit from Short Line Tax Credit	$ 6,300,000
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				$ 2,520,000	$ 2,270,000
Non-current deferred income tax liabilities				983,925,000	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)