Defined Contribution 401(k) Plan (Details) $ in Millions	4 Months Ended	12 Months Ended
	Apr. 30, 2016	Dec. 31, 2017 USD ($) defined_contribution_plan	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, number of plans | defined_contribution_plan		3
Defined contribution 401(k) plan, requisite service period		60 days
Defined contribution 401(k) plan, requisite age		21 years
Defined contribution 401(k) plan, matching contributions made in period | $		$ 19.6	$ 16.2	$ 12.5
Employee Retirement Savings Plan | Flight Attendants and Dispatchers
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	50.00%	100.00%
Employee Retirement Savings Plan | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match		50.00%
Employee Retirement Savings Plan | Maximum | Flight Attendants and Dispatchers
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation	6.00%	6.00%
Employee Retirement Savings Plan | Maximum | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation		6.00%
Pilots’ Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match		100.00%
Pilots’ Retirement Savings Plan | Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation		9.00%
Puerto Rico Retirement Savings Plan | Pilots
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match		100.00%
Puerto Rico Retirement Savings Plan | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match		50.00%
Puerto Rico Retirement Savings Plan | Maximum | Pilots
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation		9.00%
Puerto Rico Retirement Savings Plan | Maximum | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation		6.00%