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Nature of Operations and Significant Accounting Policies - Narrative (Details) mi in Thousands, $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2017 USD ($) | Sep. 30, 2018 state mi | Mar. 31, 2018 USD ($)
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 |
Advisory Fees Related to Shareholder Matters |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Incurred cost | $ 1 |  |
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

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