v3.25.2
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2025
Aug. 06, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Securities Act File Number 0-21719  
Entity Registrant Name Steel Dynamics, Inc.  
Entity Incorporation, State or Country Code IN  
Entity Tax Identification Number 35-1929476  
Entity Address, Address Line One 7575 West Jefferson Blvd  
Entity Address, City or Town Fort Wayne  
Entity Address, State or Province IN  
Entity Address, Postal Zip Code 46804  
City Area Code 260  
Local Phone Number 969-3500  
Title of 12(b) Security Common Stock voting, $0.0025 par value  
Trading Symbol STLD  
Security Exchange Name NASDAQ  
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  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   147,204,589
Entity Central Index Key 0001022671  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Amendment Flag false