Fair Value of Financial Instruments Financial instruments Carried at Fair Value-Level 3 (Details) - Heart of Georgia Railroad [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
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	$ 100
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Accrued deferred consideration	$ 6,100	$ 5,974