Commitments and Contingencies - Future Delivery Commitments (Detail)	12 Months Ended
	Dec. 31, 2018 MMBTU / d bbl / d
2019 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	347,935
2019 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	74,000
2020 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	292,845
2020 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	71,492
2021 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	138,011
2021 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	55,932
2022 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	83,535
2022 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	43,000
2023 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	2,628
2023 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	35,000
2024 - 2028 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	0
2024 - 2028 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	35,000
2029 - 2031 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	0
2029 - 2031 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	20,000