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v3.22.1

Financing: Debt Covenants (Details) | Mar. 31, 2022
--- | ---
Line of Credit Facility [Line Items] |
Consolidated Indebtedness to Capitalization Ratio | 0.610
Maximum |
Line of Credit Facility [Line Items] |
Consolidated Indebtedness to Capitalization Ratio | 0.65
Maximum | Wyoming Electric |
Line of Credit Facility [Line Items] |
Consolidated Indebtedness to Capitalization Ratio | 0.60

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- Definition Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year + References No definition available. + Details
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Namespace Prefix: | bkh_
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Balance Type: | na
Period Type: | instant

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- 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 No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=bkh_WyomingElectricMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |