The charge against earnings in the period to reduce the carrying amount of real property to fair value.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

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

Impairment (Details)		3 Months Ended		9 Months Ended
Impairment (Details)	Jun. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / bbl	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / bbl	Sep. 30, 2020 USD ($)	Sep. 30, 2021 MMcf
Impaired Long-Lived Assets Held and Used [Line Items]
Commodity price (usd per unit)		57.69		57.69		2.94
Full cost ceiling limitation impairment		$ 0		$ 0	$ 215,800,000
Impairment charge			$ 44,000,000		253,800,000
Disposal Group, Held-for-sale, Not Discontinued Operations \| Corporate Headquarters Building
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment charge	$ 38,000,000				$ 38,000,000