Debt and Other Obligations - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2015 USD ($) aircraft trust	Dec. 31, 2015 USD ($) agreement aircraft	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Number of facility agreements | agreement		2
Repayments of principal		$ 25.4	$ 0.0
Corporate credit cards
Line of Credit Facility [Line Items]
Maximum borrowing capacity		18.6	18.6
Line of credit, outstanding		7.3	4.5
Aircraft fuel
Line of Credit Facility [Line Items]
Maximum borrowing capacity		38.0	38.0
Line of credit, outstanding		$ 6.9	$ 9.3
Senior loans
Line of Credit Facility [Line Items]
Debt instrument, term		12 years
Annual commitment fee (percent)			0.75%
Junior loans
Line of Credit Facility [Line Items]
Debt instrument, term		7 years
Annual commitment fee (percent)			1.25%
Airbus | A320
Line of Credit Facility [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft	3
Airbus | A321 | Enhanced Equipment Trust Certificate
Line of Credit Facility [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft		3
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft	12
Airbus | A320 and A321 | Enhanced Equipment Trust Certificate
Line of Credit Facility [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		12
Enhanced Equipment Trust Certificate
Line of Credit Facility [Line Items]
Long-term debt outstanding		$ 120.8
Weighted average interest rate	4.15%
Enhanced Equipment Trust Certificate | Equipment Notes, Series A [Member]
Line of Credit Facility [Line Items]
State interest rate percentage		4.10%
Enhanced Equipment Trust Certificate | Equipment Notes, Series B [Member]
Line of Credit Facility [Line Items]
State interest rate percentage		4.45%
Enhanced Equipment Trust Certificate | Aircraft and Related Flight Equipment
Line of Credit Facility [Line Items]
Number of Trusts | trust	2
Face amount, commitment for future issuance	$ 576.6	$ 455.8
Framework Agreement [Member]
Line of Credit Facility [Line Items]
Long-term debt outstanding		$ 379.0
Commitment fees			$ 0.7
Framework Agreement [Member] | Airbus | A320
Line of Credit Facility [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft		7
Framework Agreement [Member] | Airbus | A321
Line of Credit Facility [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft		3
Facility Agreement [Member]
Line of Credit Facility [Line Items]
Long-term debt outstanding		$ 185.0
Facility Agreement [Member] | Airbus | A320
Line of Credit Facility [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft		5