Derivative Instruments and Fair Value Measurements - Summary of Fair Value of Open Commodity Derivatives (Detail) - Commodity Derivatives [Member] - USD ($) $ in Thousands |
Sep. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Unrealized Gain on Commodity Derivatives [Member] | ||
| Derivatives Fair Value [Line Items] | ||
| Derivatives not designated as hedging instruments, fair value of assets derivative | $ 1,057 | $ 6,737 |
| Unrealized Loss on Commodity Derivatives [Member] | ||
| Derivatives Fair Value [Line Items] | ||
| Derivatives not designated as hedging instruments, fair value of Liability derivative | $ (2,594) |