Commitments and Contingencies - Future Delivery Commitments (Detail)	12 Months Ended
	Dec. 31, 2017 MMBTU / d bbl / d
2018 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	382,534
2018 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	71,000
2019 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	364,356
2019 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	55,932
2020 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	252,878
2020 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	48,625
2021 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	116,189
2021 | Ethane and Propane
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | bbl / d	48,000
2022 | Natural Gas
Commitments And Contingencies Disclosure [Line Items]
Oil and Gas Delivery Commitments and Contracts, Daily Production | MMBTU / d	68,712
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	0
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