Supplemental Information on Oil and Natural Gas Properties (Unaudited) (Costs Incurred) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquisition costs:
Evaluated properties	$ 0	$ 49,572	$ 347,305
Unevaluated properties	30,696	107,347	466,816
Development costs	379,900	189,259	259,410
Exploration costs	122,865	309,013	323,458
Total costs incurred	$ 533,461	$ 655,191	$ 1,396,989

No definition available.

Name:	us-gaap_CostsIncurredAcquisitionOfOilAndGasPropertiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have proved reserves.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62038-109447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62014-109447

+ Details

Name:	us-gaap_CostsIncurredAcquisitionOfOilAndGasPropertiesWithProvedReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have unproved reserves.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62014-109447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62038-109447

+ Details

Name:	us-gaap_CostsIncurredAcquisitionOfUnprovedOilAndGasProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

+ References

+ Details

Name:	us-gaap_CostsIncurredDevelopmentCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

+ References

+ Details

Name:	us-gaap_CostsIncurredExplorationCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of costs incurred related to oil and gas property acquisition, exploration and development activities, including capitalized costs and costs charged to expense.

+ References

No definition available.

+ Details

Name:	us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration