Commitments and Contingencies - Employees (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Sep. 30, 2019 USD ($) employee_group	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) employee_group	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]
Special charges (credits)		$ 0	$ (686)	$ 0	$ 88,656
Air Line Pilots Association, International [Member]
Concentration Risk [Line Items]
Term of collective bargaining agreement	5 years
Health Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Accrued health care claims		$ 4,700		$ 4,700		$ 4,400
Pilots [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Ratification Incentive					80,200
Adjustments for contractual provisions					8,500
Special charges (credits)					$ 88,700
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member]
Concentration Risk [Line Items]
Number of union-represented employee groups | employee_group		5		5
Company's employees covered under collective bargaining agreements (as a percent)				80.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Air Line Pilots Association, International [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)				26.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Association of Flight Attendants [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)				46.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Professional Airline Flight Control Association [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)				1.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | International Association Of Machinists And Aerospace Workers (IAM) [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)				3.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Transport Workers Union [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)				3.00%