v3.26.3
SHARE-BASED COMPENSATION - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share‑based compensation $ 5,880 $ 5,433 $ 16,792 $ 15,691
Restricted Stock        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share‑based compensation 5,900 $ 5,400 16,800 $ 15,700
Share-based payment arrangement, nonvested award, excluding option, cost not yet recognized, amount $ 44,700   $ 44,700  
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition (in years)     2 years 8 months 12 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