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Financing: Debt Covenants (Additional Information) (Details)	Sep. 30, 2023
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.61
Maximum
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.65
Wyoming Electric
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.53
Wyoming Electric | Maximum
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.6

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

+ Details

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Balance Type:	na
Period Type:	duration

X

- Definition

Indebtedness divided by net capital.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=bkh_WyomingElectricMember
Namespace Prefix:
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