Fair Value Measurements - Quantative Information about Level 3 Fair Value (Details) - Option Model - Implied Volatility - Fuel derivatives	Jun. 30, 2016
Third Quarter 2016
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	20.00%
Fair Value Measurement Range, Maximum	34.00%
Fourth Quarter 2016
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	27.00%
Fair Value Measurement Range, Maximum	36.00%
2017
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	27.00%
Fair Value Measurement Range, Maximum	39.00%
2018
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	23.00%
Fair Value Measurement Range, Maximum	32.00%