XML 100 R89.htm IDEA: XBRL DOCUMENT v3.25.0.1

Employee Benefit Plans: Defined Benefit Pension Plan (Details) - PensionPlan	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Number of Defined Pension Plans		1
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		100.00%	100.00%
Return Seeking Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		30.00%	24.00%
Liability-hedging Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		70.00%	76.00%
Investment in privately held oil and gas company | Return Seeking Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		19.00%	14.00%
Real Estate | Return Seeking Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		5.00%	5.00%
Fixed Income | Return Seeking Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		3.00%	2.00%
Fixed Income | Liability-hedging Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		68.00%	74.00%
Hedge Funds | Return Seeking Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		3.00%	3.00%
Cash | Liability-hedging Assets
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%	2.00%
Minimum | Return Seeking Assets | Pension Plan
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		20.00%
Minimum | Return Seeking Assets | Pension Plan | Scenario Forecast
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	26.00%
Minimum | Hedge Funds | Pension Plan
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		72.00%
Minimum | Hedge Funds | Pension Plan | Scenario Forecast
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	66.00%
Maximum | Return Seeking Assets | Pension Plan
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		28.00%
Maximum | Return Seeking Assets | Pension Plan | Scenario Forecast
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	34.00%
Maximum | Hedge Funds | Pension Plan
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		80.00%
Maximum | Hedge Funds | Pension Plan | Scenario Forecast
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	74.00%

X

- Definition

Number of Defined Pension Plans

+ References

No definition available.

+ Details

Name:	bkh_NumberOfDefinedPensionPlans
Namespace Prefix:	bkh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_EquitySecuritiesByInvestmentObjectiveAxis=bkh_ReturnSeekingAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_EquitySecuritiesByInvestmentObjectiveAxis=bkh_LiabilityHedgingAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_HedgeFundsMultistrategyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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