Commitments and Contingencies (Environmental Compliance) (Details) - Fort Berthold Indian Reservation - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Dec. 31, 2021
Site Contingency [Line Items]
Accrual of environmental loss contingencies	$ 0.9	$ 1.0
Maximum
Site Contingency [Line Items]
Potential liability for environmental exposures	1.8
Minimum
Site Contingency [Line Items]
Potential liability for environmental exposures	$ 0.9

Total costs accrued as of the balance sheet date for environmental loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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Balance Type:	credit
Period Type:	instant