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Cover - USD ($)
 12 Months Ended
Dec. 31, 2020
Feb. 16, 2021
Jun. 30, 2020
Entity Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2020    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-37976    
Entity Registrant Name Southwest Gas Holdings, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 81-3881866    
Entity Address, Address Line One 8360 S. Durango Dr.    
Entity Address, Address Line Two Post Office Box 98510    
Entity Address, City or Town Las Vegas,    
Entity Address, State or Province NV    
Entity Address, Postal Zip Code 89193-8510    
City Area Code (702)    
Local Phone Number 876-7237    
Title of 12(b) Security Southwest Gas Holdings, Inc. Common Stock, $1 par value    
Trading Symbol SWX    
Security Exchange Name NYSE    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Well-known Seasoned Issuer 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     $ 3,860,578,802
Entity Common Stock, Shares Outstanding   57,225,776  
Entity Central Index Key 0001692115    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Amendment Flag false    
Documents Incorporated by Reference
Description Part Into Which Incorporated
Annual Report to Stockholders for the Year Ended 
December 31, 2020
2021 Proxy Statement
 
Parts I, II, and IV

Part III
    
Southwest Gas Corporation      
Entity Information [Line Items]      
Document Type 10-K    
Document Period End Date Dec. 31, 2020    
Current Fiscal Year End Date --12-31    
Entity File Number 1-7850    
Entity Registrant Name Southwest Gas Corporation    
Entity Incorporation, State or Country Code CA    
Entity Tax Identification Number 88-0085720    
Entity Address, Address Line One 8360 S. Durango Dr.    
Entity Address, Address Line Two Post Office Box 98510    
Entity Address, City or Town Las Vegas,    
Entity Address, State or Province NV    
Entity Address, Postal Zip Code 89193-8510    
City Area Code (702)    
Local Phone Number 876-7237    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Well-known Seasoned Issuer No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag false    
Entity Shell Company false    
Entity Central Index Key 0000092416    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Amendment Flag false