Commitments and Contingencies - Concentration Risks and Employees Under Collective Bargaining Agreements (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Concentration Risk and Significant Customers
Allowance for doubtful accounts | $		$ 157,000	$ 173,000
ExpressJet Delaware Mechanics | Subsequent event
Concentration Risk and Significant Customers
Labor agreement, contract extension term (in years)	1 year
Revenue from rights, concentration risk | Customer concentration risk | Delta, United, and Continental Combined
Concentration Risk and Significant Customers
Concentration risk (as a percent)		78.80%	85.40%	86.90%
Full-time equivalent number of employees
Concentration Risk and Significant Customers
Number of employees		16,300
Full-time equivalent number of employees | Unionized employees
Concentration Risk and Significant Customers
Concentration risk (as a percent)		22.00%
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Pilots
Concentration Risk and Significant Customers
Number of employees		669
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Flight Attendants
Concentration Risk and Significant Customers
Number of employees		552
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Flight Controllers
Concentration Risk and Significant Customers
Number of employees		25
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Mechanics
Concentration Risk and Significant Customers
Number of employees		102
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Stock Clerks
Concentration Risk and Significant Customers
Number of employees		29
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Pilots
Concentration Risk and Significant Customers
Number of employees		1,111
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Flight Attendants
Concentration Risk and Significant Customers
Number of employees		618
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Mechanics
Concentration Risk and Significant Customers
Number of employees		418
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Dispatchers
Concentration Risk and Significant Customers
Number of employees		22
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Stock Clerks
Concentration Risk and Significant Customers
Number of employees		42