Summary of Significant Accounting Policies - Derivative Instruments (Details) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) aircraft derivative_instrument	Dec. 31, 2015 derivative_instrument
Airbus A321
Derivative [Line Items]
Number of aircraft protected by interest rate derivatives scheduled for delivery	3
2015 | Airbus A321
Derivative [Line Items]
Number of aircraft protected by interest rate derivatives scheduled for delivery	3
Interest rate swap
Derivative [Line Items]
Number of interest rate derivatives settled | derivative_instrument	6	6
Notional amount | $	$ 120