Regulatory Matters - Summary of Risk-Based Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
S&T
Leverage Ratio, Amount
Actual	$ 1,154,736	$ 1,112,126
Minimum Regulatory Capital Requirements	379,316	371,211
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 474,146	$ 464,014
Leverage Ratio, Ratio
Actual	0.1218	0.1198
Minimum Regulatory Capital Requirements	0.0400	0.0400
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0500	0.0500
Common Equity Tier 1 ratio, Amount
Actual	$ 1,130,736	$ 1,088,126
Minimum Regulatory Capital Requirements	355,419	335,888
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 513,383	$ 485,172
Common Equity Tier 1 ratio, Ratio
Actual	0.1432	0.1458
Minimum Regulatory Capital Requirements	0.0450	0.0450
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0650	0.0650
Tier 1 Capital (to Risk-Weighted Assets), Amount
Actual	$ 1,154,736	$ 1,112,126
Minimum Regulatory Capital Requirements	473,892	447,851
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 631,856	$ 597,134
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1462	0.1490
Minimum Regulatory Capital Requirements	0.0600	0.0600
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0800	0.0800
Total Capital (to Risk-Weighted Assets), Amount
Actual	$ 1,278,474	$ 1,230,497
Minimum Regulatory Capital Requirements	631,856	597,134
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 789,821	$ 746,418
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1619	0.1649
Minimum Regulatory Capital Requirements	0.0800	0.0800
To be Well Capitalized Under Prompt Corrective Action Provisions	0.1000	0.1000
S&T Bank
Leverage Ratio, Amount
Actual	$ 1,128,495	$ 1,060,010
Minimum Regulatory Capital Requirements	379,139	371,002
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 473,923	$ 463,752
Leverage Ratio, Ratio
Actual	0.1191	0.1143
Minimum Regulatory Capital Requirements	0.0400	0.0400
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0500	0.0500
Common Equity Tier 1 ratio, Amount
Actual	$ 1,128,495	$ 1,060,010
Minimum Regulatory Capital Requirements	355,206	335,722
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 513,076	$ 484,932
Common Equity Tier 1 ratio, Ratio
Actual	0.1430	0.1421
Minimum Regulatory Capital Requirements	0.0450	0.0450
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0650	0.0650
Tier 1 Capital (to Risk-Weighted Assets), Amount
Actual	$ 1,128,495	$ 1,060,010
Minimum Regulatory Capital Requirements	473,608	447,629
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 631,478	$ 596,839
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1430	0.1421
Minimum Regulatory Capital Requirements	0.0600	0.0600
To be Well Capitalized Under Prompt Corrective Action Provisions	0.0800	0.0800
Total Capital (to Risk-Weighted Assets), Amount
Actual	$ 1,252,175	$ 1,178,335
Minimum Regulatory Capital Requirements	631,478	596,839
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 789,347	$ 746,049
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1586	0.1579
Minimum Regulatory Capital Requirements	0.0800	0.0800
To be Well Capitalized Under Prompt Corrective Action Provisions	0.1000	0.1000