Debt and Other Obligations - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 2,213.6	$ 2,234.5
Long-term debt, current maturities	214.0	162.8
Long-term debt, excluding current maturities	1,959.2	2,024.0
Corporate credit cards
Line of Credit Facility [Line Items]
Maximum borrowing capacity	33.6	33.6
Line of credit, current	4.6	3.5
Lines of Credit with Counterparties for Jet Fuel and Derivatives [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	41.5	41.5
Aircraft fuel
Line of Credit Facility [Line Items]
Line of credit, current	$ 25.3	23.0
Fixed-rate term loans \| Maximum
Line of Credit Facility [Line Items]
Long-term Debt, Term	12 years
Fixed-rate term loans \| Minimum
Line of Credit Facility [Line Items]
Long-term Debt, Term	11 years
Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 160.0	135.3
Long-term debt, current maturities	50.0
Long-term debt, excluding current maturities	110.0
Fixed-rate term loans
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 778.2	$ 625.1
Fixed-rate term loans \| Fixed-rate term loans \| Maximum
Line of Credit Facility [Line Items]
Stated interest rate percentage	3.93%
Fixed-rate term loans \| Fixed-rate term loans \| Minimum
Line of Credit Facility [Line Items]
Stated interest rate percentage	2.85%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Period between issuance and maturity of long-term debt, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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