Basis of Presentation and Consolidation (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings	$ (635,438)		$ (633,496)	$ (570,406)
Rail Group | Revenues under ASC 606 | Assets, Net
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in net assets		$ 25,600
Rail Group | Revenues under ASC 606 | Financing Obligations
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in financing liabilities and deferred tax liabilities		34,000
ASC 606 Impact | Revenues under ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings	$ (8,475)
ASC 606 Impact | Rail Group | Revenues under ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings		$ 8,400