Regulatory Matters - Summary of Risk-Based Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
S&T
Leverage Ratio, Amount
Actual	$ 967,708	$ 889,785
Minimum Regulatory Capital Requirements	349,914	365,535
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 437,392	$ 456,918
Leverage Ratio
Actual	0.1106	0.0974
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 (to Risk-Weighted Assets), Amount
Actual	$ 938,708	$ 860,785
Minimum Regulatory Capital Requirements	329,701	322,109
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 476,235	$ 465,268
Common Equity Tier 1 (to Risk-Weighted Assets), Ratio
Actual	0.1281	0.1203
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	$ 967,708	$ 889,785
Minimum Regulatory Capital Requirements	439,602	429,479
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 586,135	$ 572,638
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1321	0.1243
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	$ 1,078,897	$ 987,420
Minimum Regulatory Capital Requirements	586,135	572,638
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 732,669	$ 715,798
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1473	0.1379
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	$ 938,377	$ 864,127
Minimum Regulatory Capital Requirements	349,746	365,544
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 437,182	$ 456,930
Leverage Ratio
Actual	0.1073	0.0946
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 (to Risk-Weighted Assets), Amount
Actual	$ 938,377	$ 864,127
Minimum Regulatory Capital Requirements	329,565	321,711
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 476,038	$ 464,694
Common Equity Tier 1 (to Risk-Weighted Assets), Ratio
Actual	0.1281	0.1209
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	$ 938,377	$ 864,127
Minimum Regulatory Capital Requirements	439,420	428,948
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 585,893	$ 571,931
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1281	0.1209
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	$ 1,049,566	$ 961,762
Minimum Regulatory Capital Requirements	585,893	571,931
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 732,367	$ 714,913
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1433	0.1345
Minimum Regulatory Capital Requirements	0.0800	0.0800
To be Well Capitalized Under Prompt Corrective Action Provisions	0.1000	0.1000