Derivative Instruments - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) bbl $ / bbl Entity	Dec. 31, 2018 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Document Period End Date	Mar. 31, 2019
Derivative assets	$ 31,257	$ 991
Second Quarter 2019 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,421
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.48
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 3,361
Second Quarter 2019 [Member] | Louisiana Light Sweet [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-LLS
Derivative, Nonmonetary Notional Amount | bbl	5,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	59.17
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 3,109
Second Quarter 2019 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	1000
Derivative, Nonmonetary Notional Amount | $ / bbl	64.00
Derivative, Swap Type, Average Fixed Price | $ / bbl	0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 183
Commodity contracts
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative assets	$ 28,400
Number of derivative counterparties | Entity	7
Commodity contracts | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Third-party quoted forward prices	WTI
Commodity contracts | Louisiana Light Sweet [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Third-party quoted forward prices	LLS
Commodity contracts | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Third-party quoted forward prices	MEH
Third Quarter 2019 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,397
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.50
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 3,430
Third Quarter 2019 [Member] | Louisiana Light Sweet [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-LLS
Derivative, Nonmonetary Notional Amount | bbl	5,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	59.17
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 2,592
Third Quarter 2019 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	1,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	64.00
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 34
Fourth Quarter 2019 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,398
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.50
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 3,130
Fourth Quarter 2019 [Member] | Louisiana Light Sweet [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-LLS
Derivative, Nonmonetary Notional Amount | bbl	5,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	59.17
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 1,995
Fourth Quarter 2019 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	1,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	64.00
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 68
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 0
First Quarter 2020 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.09
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 2,904
First Quarter 2020 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	2,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	61.03
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 58
Second Quarter 2020 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.09
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 2,369
Second Quarter 2020 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	2,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	61.03
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 57
Third Quarter 2020 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.09
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 1,898
Third Quarter 2020 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	2,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	61.03
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 40
Fourth Quarter 2020 [Member] | Crude Oil
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Type of Instrument	Swaps-WTI
Derivative, Nonmonetary Notional Amount | bbl	6,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	54.09
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 1,518
Fourth Quarter 2020 [Member] | MEH [Domain]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative, Nonmonetary Notional Amount | bbl	2,000
Derivative, Swap Type, Average Fixed Price | $ / bbl	61.03
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	$ 39