Recent Accounting Developments	9 Months Ended
Recent Accounting Developments	Sep. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Developments	Recent Accounting Developments Recently Adopted Accounting Pronouncements Leases The Company adopted ASU No. 2016-02, "Leases (Topic 842)," effective January 1, 2019. The Company adopted Topic 842 utilizing the modified retrospective adoption method with an effective date of January 1, 2019 and elected the package of transition practical expedients for expired or existing contracts, which does not require reassessment of: (1) whether any of the Company's contracts are or contain leases, (2) lease classification and (3) initial direct costs. Therefore, the condensed financial statements for 2019 are presented under the new standard, while the comparative periods presented are not adjusted and continue to be reported in accordance with the Company's historical accounting policy. This standard requires all lessees to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, for all leases with a term greater than 12 months. The adoption of the new lease standard had a significant impact on the Company's condensed balance sheets due to the recognition of $1.0 billion of right-of-use assets for operating leases, $128.1 million of current maturities of operating leases and $895.1 million of operating leases, less current maturities. In addition, the Company recognized a $5.5 million cumulative effect adjustment, net of tax, to retained earnings. This adjustment was driven by the recognition of unamortized deferred gains and losses related to aircraft sale-leaseback transactions entered into in prior periods. Prior to the adoption of Topic 842, gains and losses on sale-leaseback transactions were generally deferred and recognized in income over the lease term. The accounting for finance leases is substantially unchanged. The adoption of Topic 842 did not have a significant impact on the Company's lease classification or a material impact on its statements of operations and liquidity. Additionally, the adoption of Topic 842 did not have a material impact on the Company’s debt-covenant compliance under its current agreements. Refer to Note 10, Leases for information regarding the Company's adoption of Topic 842 and the Company's undiscounted future lease payments and the timing of those payments. Recently Issued Accounting Pronouncements Not Yet Adopted Cloud Computing Arrangements In August 2018, the FASB issued ASU No. 2018-15, "Intangibles - Goodwill and Other - Internal-Use Software." This new standard requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in Accounting Standards Codification ("ASC") 350-40, "Accounting for Internal-Use Software," to determine which implementation costs to capitalize as assets and amortize over the term of the hosting arrangement or expense as incurred. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2020. Early adoption is permitted, including during an interim period. The Company has elected not to early adopt. Entities have the option to apply this standard prospectively to all implementation costs incurred after the date of adoption or retrospectively. The Company is evaluating this new standard, but does not expect it to have a significant impact on its financial statement presentation or results. 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 rather than as reductions to the 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 has elected not to early adopt. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statement presentation or results.