Recent Accounting Developments	9 Months Ended
Recent Accounting Developments	Sep. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Developments	Recent Accounting Developments Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (the FASB) issued Accounting Standards Update (ASU) No. 2014-09, (ASU 2014-09) "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The new guidance is effective for the Company in the first quarter of 2018. Entities have the option to use either a full retrospective or a modified retrospective approach to adopt ASU 2014-09. The Company currently anticipates utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented, and plans to adopt the standard as of January 1, 2018. While the Company is still evaluating the impact, it currently believes the most significant impact of this ASU will be the elimination of the incremental cost method for frequent flier program accounting, which will require the Company to re-value and record a liability associated with customer flight miles earned as part of the Company’s frequent flier program with a relative fair value approach. While our evaluation is ongoing, the Company currently estimates that applying a relative fair value would increase its air traffic liability by approximately $10 million at the date of adoption. The Company also expects the classification and timing of recognition of certain ancillary fees to be impacted by the adoption of ASU 2014-09. While the Company believes the adoption will not have a significant impact on earnings, the classification of certain revenues, such as bags, seats and other travel-related fees may be deemed part of the single performance obligation of providing passenger transportation. The Company expects that these revenues currently classified as non-ticket revenue, approximately $1 billion annually, will be reclassified to passenger revenue after adoption. Financial Instruments In January 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10).” ASU 2016-01 makes several modifications to Subtopic 825-10 including the elimination of the available-for-sale classification of equity investments, and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. ASU 2016-01 is effective for the Company for interim and annual periods beginning January 1, 2018 and is not expected to have a material impact on the Company’s financial statements. Leases In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)." This standard will require all leases with durations greater than twelve months to be recognized on the condensed balance sheet and is effective for the Company in the first quarter of 2019, with early adoption permitted. The Company is currently evaluating the new guidance and believes adoption of this standard will have a significant impact on its condensed balance sheets although adoption is not expected to significantly change the recognition, measurement or presentation of lease expenses within the statements of operations and cash flows. See Note 8, Commitments and Contingencies for information regarding the Company's undiscounted future lease payments and the timing of those payments. Share-Based Compensation In March 2016, the FASB issued ASU No. 2016-09, "Improvements to Employee Share-Based Payment Accounting," which simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification on the statement of cash flows. The Company adopted this guidance on January 1, 2017. As a result, excess income tax benefits and deficiencies related to share-based compensation are now included within income tax expense rather than additional paid in capital. For the nine months ended September 30, 2017, $0.6 million of income tax deficiency related to share-based compensation was included within income tax expense on the Company's statements of operations. Additionally, excess income tax benefits and deficiencies for share-based payments are now included in net operating cash flows rather than net financing cash flows. The changes have been applied prospectively in accordance with the guidance and prior periods have not been adjusted. Accounting for Credit Losses In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses." The standard requires the use of an "expected loss" model on certain types of financial instruments. The standard also amends the impairment model for available-for-sale securities and requires estimated credit losses to be recorded as allowances instead of reductions to amortized cost of the securities. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2020, with early adoption permitted. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statements. Statement of Cash Flows In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows." The standard is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2018, with early adoption permitted. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statements.