Fair Value - Quantitative Information About Level Three Fair Value Measurements (Detail) - Fuel price derivatives – diesel [Member] $ in Thousands |
9 Months Ended |
|---|---|
|
Sep. 30, 2015
USD ($)
$ / gal
| |
| Fair Value Inputs, Assets, Quantitative Information [Line Items] | |
| Fair Value | $ | $ 4,445 |
| Option Model [Member] | Minimum [Member] | |
| Fair Value Inputs, Assets, Quantitative Information [Line Items] | |
| Future retail price of diesel (in dollars per gallon) | 3.72 |
| Option Model [Member] | Maximum [Member] | |
| Fair Value Inputs, Assets, Quantitative Information [Line Items] | |
| Future retail price of diesel (in dollars per gallon) | 3.85 |