Nature of Operations and Significant Accounting Policies - Narrative (Details) mi in Thousands, $ in Millions	Mar. 31, 2018 USD ($) state mi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total number of rail route miles | mi	21
Number of states rail network serves | state	23
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification adjustment	$ 107
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification adjustment	$ (107)