v3.26.1
Summary of Significant Accounting Policies - Fair Value Measurements (Details) - EBP 002 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments $ 144,188,868 $ 128,354,635
Money market fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 6,767,841 7,491,492
Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 123,475,784 107,035,758
S&T Bancorp, Inc. common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 13,945,243 13,827,385
Total    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 144,188,868 128,354,486
Total | Money market fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 6,767,841 7,491,343
Total | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 123,475,784 107,035,758
Total | S&T Bancorp, Inc. common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 13,945,243 13,827,385
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 144,188,868 128,354,486
Level 1 | Money market fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 6,767,841 7,491,343
Level 1 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 123,475,784 107,035,758
Level 1 | S&T Bancorp, Inc. common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 13,945,243 13,827,385
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 2 | Money market fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 2 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 2 | S&T Bancorp, Inc. common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 3 | Money market fund    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 3 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments 0 0
Level 3 | S&T Bancorp, Inc. common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments $ 0 $ 0