Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($) employee_group	Dec. 31, 2015 USD ($) employee_group	Dec. 31, 2014 USD ($)
Concentration Risk [Line Items]
Marketing and advertising expenses \| $	$ 3.2	$ 3.5	$ 3.0
Aircraft fuel expenditure concentration risk \| Total operating expenses
Concentration Risk [Line Items]
Concentration of risk	24.00%	28.00%	39.00%
Unionized employees concentration risk \| Number of employees, total
Concentration Risk [Line Items]
Concentration of risk	73.00%	73.00%
Union-represented employee groups \| employee_group	4	4

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

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