Inventories - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Petroleum, Natural Gas and Asphalt Inventory | |||
| Public Utilities, Inventory [Line Items] | |||
| Provision for inventory write-down | $ 1.7 | $ 27.9 | $ 50.5 |