Income Taxes (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income tax provision	$ 18,866,000	$ 26,446,000	$ 33,126,000	$ 10,556,000
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions		$ 4,800,000		$ 4,800,000
Effective income tax rate	26.90%		26.90%
Tax Benefit from United States Short Line Tax Credit, Amount			$ 31,600,000
Effective income tax reconciliation excluding short line tax credit, percentage		29.80%
Effective income tax reconciliation excluding short line tax credit and prior period portion of the reserve for uncertain tax positions, percentage				28.50%
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
April 1, 2018 through June 30, 2018
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions		$ 700,000		$ 700,000
January 1, 2018 through March 31, 2018
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions		400,000		400,000
March 25, 2015 through December 31, 2017
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions		$ 3,700,000		$ 3,700,000