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Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2020
Jan. 31, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Current Fiscal Year End Date --12-31    
Document Period End Date Dec. 31, 2020    
Document Transition Report false    
Entity File Number 001-31303    
Entity Registrant Name BLACK HILLS CORPORATION    
Entity Incorporation, State or Country Code SD    
Entity Tax Identification Number 46-0458824    
Entity Address, Address Line One 7001 Mount Rushmore Road    
Entity Address, City or Town Rapid City    
Entity Address, State or Province SD    
Entity Address, Postal Zip Code 57702    
City Area Code 605    
Local Phone Number 721-1700    
Title of 12(b) Security Common stock of $1.00 par value    
Trading Symbol BKH    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 3,528,768,075
Entity Common Stock, Shares Outstanding   62,794,490  
Documents Incorporated by Reference Portions of the registrant’s Definitive Proxy Statement being prepared for the solicitation of proxies in connection with the 2021 Annual Meeting of Stockholders to be held on April 27, 2021, are incorporated by reference in Part III of this Form 10-K.    
Entity Central Index Key 0001130464    
Amendment Flag false    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY