Financial Instruments - Outstanding Fuel Hedges (Details) - Fuel Hedges Remaining 2018 |
Jun. 30, 2018
gal
$ / gal
|
|---|---|
| Derivative [Line Items] | |
| Gallons Hedged (in gallons per year) | gal | 3,750,000 |
| Weighted Average Contract Price per Gallon (in dollars per gallon) | $ / gal | 2.59 |