Regulatory Matters - Summary of Risk-Based Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
S&T
Leverage Ratio, Amount
Actual	$ 1,034,828	$ 967,708
Minimum Regulatory Capital Requirements	369,297	349,914
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 461,621	$ 437,392
Leverage Ratio, Ratio
Actual	0.1121	0.1106
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	$ 1,010,828	$ 938,708
Minimum Regulatory Capital Requirements	340,159	329,701
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 491,341	$ 476,235
Common Equity Tier 1 ratio, Ratio
Actual	0.1337	0.1281
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	$ 1,034,828	$ 967,708
Minimum Regulatory Capital Requirements	453,545	439,602
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 604,727	$ 586,135
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1369	0.1321
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	$ 1,154,376	$ 1,078,897
Minimum Regulatory Capital Requirements	604,727	586,135
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 755,909	$ 732,669
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1527	0.1473
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	$ 995,824	$ 938,377
Minimum Regulatory Capital Requirements	369,133	349,746
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 461,416	$ 437,182
Leverage Ratio, Ratio
Actual	0.1079	0.1073
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	$ 995,824	$ 938,377
Minimum Regulatory Capital Requirements	339,954	329,565
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 491,045	$ 476,038
Common Equity Tier 1 ratio, Ratio
Actual	0.1318	0.1281
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	$ 995,824	$ 938,377
Minimum Regulatory Capital Requirements	453,272	439,420
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 604,362	$ 585,893
Tier 1 Capital (to Risk-Weighted Assets), Ratio
Actual	0.1318	0.1281
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	$ 1,115,315	$ 1,049,566
Minimum Regulatory Capital Requirements	604,362	585,893
To be Well Capitalized Under Prompt Corrective Action Provisions	$ 755,453	$ 732,367
Total Capital (to Risk-Weighted Assets), Ratio
Actual	0.1476	0.1433
Minimum Regulatory Capital Requirements	0.0800	0.0800
To be Well Capitalized Under Prompt Corrective Action Provisions	0.1000	0.1000

Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio

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Banking Regulation, Total Capital, Ratio

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480696/942-505-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
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-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480696/942-505-50-1B

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