Financial Instruments - Outstanding Fuel Hedges (Details) |
Sep. 30, 2016
gal
$ / gal
|
|---|---|
| Fuel Hedges Remaining 2016 | |
| Derivative [Line Items] | |
| Gallons hedged (in gallons per year) | gal | 6,750,000 |
| Weighted Average Contract Price per Gallon (in dollars per gallon) | $ / gal | 3.57 |
| Fuel Hedges Remaining 2017 | |
| Derivative [Line Items] | |
| Gallons hedged (in gallons per year) | gal | 12,000,000 |
| Weighted Average Contract Price per Gallon (in dollars per gallon) | $ / gal | 2.92 |
| Fuel Hedges Remaining 2018 | |
| Derivative [Line Items] | |
| Gallons hedged (in gallons per year) | gal | 3,000,000 |
| Weighted Average Contract Price per Gallon (in dollars per gallon) | $ / gal | 2.61 |