Commitments and Contingencies - Employees (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 employee_groups	Dec. 31, 2012 employee_groups
Multiemployer Plans [Line Items]
Accrued health care claims	$ 2.1	$ 1.9
Unionized employees concentration risk | Number of employees, total
Multiemployer Plans [Line Items]
Union-represented employee groups	3	3
Concentration of risk	59.00%	54.00%
Unionized employees concentration risk | Number of employees, total | Association of Flight Attendants [Member]
Multiemployer Plans [Line Items]
Concentration of risk	34.00%
Unionized employees concentration risk | Number of employees, total | Air Line Pilots Association, International [Member]
Multiemployer Plans [Line Items]
Concentration of risk	24.00%
Unionized employees concentration risk | Number of employees, total | Transport Workers Union [Member]
Multiemployer Plans [Line Items]
Concentration of risk	1.00%