Income Taxes (Details) AUD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 AUD	Sep. 30, 2016 USD ($)
Effective income tax rate	36.40%	25.70%	38.90%	29.20%
Effective Income Tax Rate Reconciliation, United States Short Line Tax Credit, Amount		$ 7,800,000		$ 21,400,000
Unrecognized Tax Benefits	$ 3,300,000		$ 3,271,000
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
Impairment of Assets [Member] | Australian Operations [Member]
Valuation allowance					AUD 2.6	$ 2,000,000
State and Local Jurisdiction [Member]
Change in enacted tax rate, amount	$ 1,400,000		$ 1,300,000
Foreign Tax Authority [Member]
Change in enacted tax rate, amount		$ 4,300,000		$ 4,272,000