Recently Issued Accounting Standards (Notes)	12 Months Ended
Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Issued Accounting Standards	RECENTLY ISSUED ACCOUNTING STANDARDS: Accounting Standards Not Yet Effective In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and includes the specific steps for recognizing revenue and disclosure requirements. In August 2015, the FASB issued ASU 2015-14, which approved a one-year deferral of the effective date of the new revenue recognition standard. In March 2016, the FASB issued ASU 2016-08, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which provides clarification when identifying performance obligations and providing implementation guidance on licensing. In May 2016, the FASB issued ASU 2016-12, which clarifies the objective of the collectibility criterion. In December 2016, the FASB issued ASU 2016-20, which provides additional clarification on contract costs, modifications and disclosures. These new standards will become effective for the Company on January 1, 2018, and the Company plans to adopt them using the modified retrospective basis. Under the new standard, the Company will continue to recognize freight revenues over time as shipments move from origin to destination, freight-related revenues and all other revenues will continue to be recognized as services are performed. For contracts that include variable consideration, the Company will be required to assess the variable consideration and recognize revenue based on estimates throughout the applicable periods. The Company is currently finalizing its review of the impact of adopting this new guidance and does not expect the adoption of this guidance to have a material impact to its consolidated financial statements or the recognition of revenue from customers, although additional disclosures will be required to help users of the financial statements understand the nature, amount and timing of revenue and cash flows arising from the Company’s contracts with customers. In January 2016, the FASB issued ASU 2016-01, Financial Instruments—Overall (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities, which requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) be measured at fair value, with subsequent changes in fair value recognized in net income. The amendments also impact certain disclosure requirements for financial instruments. The amendments will become effective for the Company beginning January 1, 2018. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which will require lessees to recognize leases on their balance sheets as a right-of-use asset with a corresponding liability. Lessees are permitted to make an accounting policy election to not recognize an asset and liability for leases with a term of 12 months or less. Additional qualitative and quantitative disclosures, including significant judgments made by management, will also be required. In January 2018, the FASB issued ASU 2018-01, which permits entities to elect an optional transition practical expedient to not evaluate under Topic 842 land easements that exist or expired before the entity's adoption of this standard and that were not previously accounted for as leases under Topic 840. These new standards will become effective for the Company beginning January 1, 2019, and will require a modified retrospective transition approach resulting in the recognition of leases as of January 1, 2017 and the retrospective adjustment of the financial statements for 2017 and 2018 when presented for comparative purposes. Early application is permitted. The Company is currently assessing the impact of adopting this guidance on its consolidated financial statements. The Company disclosed approximately $615 million in operating lease obligations in Note 6, Property and Equipment and Leases, and continues to evaluate those contracts as well as other existing arrangements to determine if they qualify for lease accounting under the new standard. The Company does not plan to adopt the standard early. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight targeted changes with respect to how cash receipts and cash payments are classified in the statements of cash flows. The amendments will become effective for the Company January 1, 2018. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated statements of cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statements of cash flows. The amendments will become effective for the Company beginning January 1, 2018. The Company does not expect the adoption of this guidance to have a material impact on its consolidated statements of cash flows. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805), Clarifying the Definition of a Business, which clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments will become effective for the Company beginning January 1, 2018. The Company will take the amendments into consideration when assessing whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. The amendments will become effective for the Company beginning January 1, 2020. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements. In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715), Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, which requires an employer to report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of the net benefit cost are required to be presented in the statement of operations separately from the service cost component and outside a subtotal of operating income, if one is presented. The amendments will become effective for the Company beginning January 1, 2018, and prior years will be reclassified to match this new presentation. As a result, the Company's operating income for the years ended December 31, 2017 and 2016 will decrease by approximately $6.4 million and $3.1 million, respectively. There is no impact to net income as a result of the adoption of this guidance. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718), Scope of Modification Accounting, which provides guidance on which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendments will become effective for the Company beginning January 1, 2018. The Company will apply this guidance to any further modifications of share-based payment awards. In August 2017, the FASB issued ASU 2017-12, Derivative and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities, which expand and refine hedge accounting for both nonfinancial and financial risk components and align the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. The amendments also include certain improvements to ease the application of current guidance related to the assessment of hedge effectiveness. The amendments will become effective for the Company beginning January 1, 2019. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220), Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The standard allows the Company to reclassify the effect of remeasuring deferred tax liabilities and assets related to items within accumulated other comprehensive income using the newly enacted federal corporate income tax rate. The amendments will become effective for the Company beginning January 1, 2019. Early adoption is permitted. The Company is evaluating the impact of the new guidance on its consolidated financial statements and related disclosure.

RECENTLY ISSUED ACCOUNTING STANDARDS:

Accounting Standards Not Yet Effective

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and includes the specific steps for recognizing revenue and disclosure requirements. In August 2015, the FASB issued ASU 2015-14, which approved a one-year deferral of the effective date of the new revenue recognition standard. In March 2016, the FASB issued ASU 2016-08, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which provides clarification when identifying performance obligations and providing implementation guidance on licensing. In May 2016, the FASB issued ASU 2016-12, which clarifies the objective of the collectibility criterion. In December 2016, the FASB issued ASU 2016-20, which provides additional clarification on contract costs, modifications and disclosures.

These new standards will become effective for the Company on January 1, 2018, and the Company plans to adopt them using the modified retrospective basis. Under the new standard, the Company will continue to recognize freight revenues over time as shipments move from origin to destination, freight-related revenues and all other revenues will continue to be recognized as services are performed. For contracts that include variable consideration, the Company will be required to assess the variable consideration and recognize revenue based on estimates throughout the applicable periods. The Company is currently finalizing its review of the impact of adopting this new guidance and does not expect the adoption of this guidance to have a material impact to its consolidated financial statements or the recognition of revenue from customers, although additional disclosures will be required to help users of the financial statements understand the nature, amount and timing of revenue and cash flows arising from the Company’s contracts with customers.

In January 2016, the FASB issued ASU 2016-01, Financial Instruments—Overall (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities, which requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) be measured at fair value, with subsequent changes in fair value recognized in net income. The amendments also impact certain disclosure requirements for financial instruments. The amendments will become effective for the Company beginning January 1, 2018. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which will require lessees to recognize leases on their balance sheets as a right-of-use asset with a corresponding liability. Lessees are permitted to make an accounting policy election to not recognize an asset and liability for leases with a term of 12 months or less. Additional qualitative and quantitative disclosures, including significant judgments made by management, will also be required. In January 2018, the FASB issued ASU 2018-01, which permits entities to elect an optional transition practical expedient to not evaluate under Topic 842 land easements that exist or expired before the entity's adoption of this standard and that were not previously accounted for as leases under Topic 840.

These new standards will become effective for the Company beginning January 1, 2019, and will require a modified retrospective transition approach resulting in the recognition of leases as of January 1, 2017 and the retrospective adjustment of the financial statements for 2017 and 2018 when presented for comparative purposes. Early application is permitted. The Company is currently assessing the impact of adopting this guidance on its consolidated financial statements. The Company disclosed approximately $615 million in operating lease obligations in Note 6, Property and Equipment and Leases, and continues to evaluate those contracts as well as other existing arrangements to determine if they qualify for lease accounting under the new standard. The Company does not plan to adopt the standard early.

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), Classification of Certain Cash Receipts and Cash Payments, which provides guidance on eight targeted changes with respect to how cash receipts and cash payments are classified in the statements of cash flows. The amendments will become effective for the Company January 1, 2018. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated statements of cash flows.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash, which requires that a statement of cash flows explain the change during the period in total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statements of cash flows. The amendments will become effective for the Company beginning January 1, 2018. The Company does not expect the adoption of this guidance to have a material impact on its consolidated statements of cash flows.

In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805), Clarifying the Definition of a Business, which clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments will become effective for the Company beginning January 1, 2018. The Company will take the amendments into consideration when assessing whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses.

In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment, which simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. The amendments will become effective for the Company beginning January 1, 2020. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715), Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, which requires an employer to report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of the net benefit cost are required to be presented in the statement of operations separately from the service cost component and outside a subtotal of operating income, if one is presented. The amendments will become effective for the Company beginning January 1, 2018, and prior years will be reclassified to match this new presentation. As a result, the Company's operating income for the years ended December 31, 2017 and 2016 will decrease by approximately $6.4 million and $3.1 million, respectively. There is no impact to net income as a result of the adoption of this guidance.

In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718), Scope of Modification Accounting, which provides guidance on which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendments will become effective for the Company beginning January 1, 2018. The Company will apply this guidance to any further modifications of share-based payment awards.

In August 2017, the FASB issued ASU 2017-12, Derivative and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities, which expand and refine hedge accounting for both nonfinancial and financial risk components and align the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. The amendments also include certain improvements to ease the application of current guidance related to the assessment of hedge effectiveness. The amendments will become effective for the Company beginning January 1, 2019. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In February 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220), Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The standard allows the Company to reclassify the effect of remeasuring deferred tax liabilities and assets related to items within accumulated other comprehensive income using the newly enacted federal corporate income tax rate. The amendments will become effective for the Company beginning January 1, 2019. Early adoption is permitted. The Company is evaluating the impact of the new guidance on its consolidated financial statements and related disclosure.