Fair Value of Financial Instruments Financial instruments Carried at Fair Value-Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Freightliner [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Loss recognized in earnings as a result of the change in estimated fair value	$ 0	$ 859	$ 0	$ 2,405
Heart of Georgia Railroad [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Loss recognized in earnings as a result of the change in estimated fair value	137	126	394	166
Fair Value, Inputs, Level 3 [Member] | Freightliner [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Accrued deferred consideration		$ 37,200		$ 37,200
Fair Value, Inputs, Level 3 [Member] | Heart of Georgia Railroad [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Accrued deferred consideration	$ 6,368		$ 6,368		$ 5,974