Derivative Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($) |
12 Months Ended | |||
|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
|
| Derivative Instruments And Hedging Activities Disclosures [Line Items] | ||||
| Impairment of oil and gas properties and equipment | $ 0 | $ 0 | $ 220,197,000 | |
| Proved oil and gas property fair value | $ 22,000,000 | |||
| Proved Property Impairment [Member] | ||||
| Derivative Instruments And Hedging Activities Disclosures [Line Items] | ||||
| Impairment of oil and gas properties and equipment | $ 0 | $ 0 | $ 214,700,000 | |