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Employee Benefit Plans: Assumptions (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Trend Year 2030 2027  
Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Trend Year 2030 2029  
Black Hills Corporation | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 for next year - All Plans 6.05% 6.10%  
Black Hills Corporation | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 for next year - All Plans 5.10% 4.92%  
Black Hills Service Company | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 Ultimate trend rate - Black Hills Corp 4.50% 4.50%  
Black Hills Service Company | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 Ultimate trend rate - Black Hills Corp 4.50% 4.50%  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 2.88% 2.56% 3.27%
Rate of increase in compensation levels 3.08% 3.34% 3.49%
Expected long-term rate of return on assets 4.50% 5.25% 6.00%
Rate of increase in compensation levels 3.34% 3.49% 3.52%
Defined Benefit Plan Assumptions Used In Calculating Net Periodic Benefit Cost Expected Rate of Return On Assets For Next Fiscal Year 4.25%    
2022 $ 26,249    
2023 27,133    
2024 27,683    
2025 28,650    
2026 28,968    
2027-2031 $ 144,422    
Pension Plan | Black Hills Corporation      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 2.56% 3.27% 4.40%
Pension Plan | Black Hills Corporation Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 for next year - All Plans 2.88%    
Supplemental Employee Retirement Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 2.77% 2.41% 3.14%
Rate of increase in compensation levels 5.00% 5.00% 5.00%
Rate of increase in compensation levels 5.00% 5.00% 5.00%
2022 $ 2,156    
2023 2,224    
2024 2,410    
2025 2,757    
2026 2,782    
2027-2031 $ 12,553    
Supplemental Employee Retirement Plan | Black Hills Corporation      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 2.41% 3.14% 4.34%
Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate 2.79% 2.41% 3.15%
Expected long-term rate of return on assets 1.80% 2.35% 3.00%
2022 $ 5,806    
2023 5,334    
2024 5,042    
2025 4,865    
2026 4,752    
2027-2031 $ 21,615    
Other Postretirement Benefits Plan | Black Hills Corporation      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 2.41% 3.15% 4.28%