Fair Value Measurements - Quantative Information about Level 3 Fair Value (Details) - Option Model - Implied Volatility - Fuel derivatives	Mar. 31, 2016
2018
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	23.00%
Fair Value Measurement Range, Maximum	32.00%
2017
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	28.00%
Fair Value Measurement Range, Maximum	41.00%
Fourth Quarter 2016
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	32.00%
Fair Value Measurement Range, Maximum	43.00%
Third Quarter 2016
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	33.00%
Fair Value Measurement Range, Maximum	43.00%
Second Quarter 2016
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	22.00%
Fair Value Measurement Range, Maximum	42.00%