Quarterly report pursuant to Section 13 or 15(d)

Document and Entity Information

Document and Entity Information - shares
6 Months Ended
Jun. 30, 2022
Aug. 04, 2022
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Jun. 30, 2022  
Securities Act File Number 001-33723  
Entity Registrant Name Main Street Capital Corporation  
Entity Incorporation, State or Country Code MD  
Entity Tax Identification Number 41-2230745  
Entity Address, State or Province TX  
Entity Address, Address Line One 1300 Post Oak Boulevard  
Entity Address, Address Line Two 8th Floor  
Entity Address, City or Town Houston  
Entity Address, Postal Zip Code 77056  
City Area Code 713  
Local Phone Number 350-6000  
Title of 12(b) Security Common Stock, par value $0.01 per share  
Trading Symbol MAIN  
Security Exchange Name NYSE  
Entity Current Reporting Status 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   73,905,636
Entity Central Index Key 0001396440  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2022  
Document Fiscal Period Focus Q2  
Amendment Flag false