Quarterly report [Sections 13 or 15(d)]

SHARE-BASED COMPENSATION - Narrative (Details)

v3.25.3
SHARE-BASED COMPENSATION - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share‑based compensation $ 5,433 $ 4,868 $ 15,691 $ 13,853
Restricted Stock        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share‑based compensation 5,400 $ 4,900 15,700 $ 13,900
Share-based payment arrangement, nonvested award, excluding option, cost not yet recognized, amount $ 40,300   $ 40,300  
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition (in years)     2 years 7 months 6 days  
Restricted Stock | Minimum        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Vesting period (in years)     3 years  
Restricted Stock | Maximum        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Vesting period (in years)     5 years  
Restricted Stock | Main Street Capital Corporation 2022 Equity and Incentive Plan | Minimum        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Vesting period (in years)     3 years  
Restricted Stock | Main Street Capital Corporation 2022 Equity and Incentive Plan | Maximum        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Vesting period (in years)     5 years