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Regulatory Matters - Summary of Risk-Based Capital Amounts and Ratios for S&T and S&T Bank (Detail) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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S&T |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Leverage Ratio, Actual Amount | $ 535,234 | $ 465,114
Leverage Ratio, Actual Ratio | 8.96% | 9.80%
Leverage Ratio, Minimum Regulatory Capital Requirements Amount | $ 238,841 | $ 189,895
Leverage Ratio, Minimum Regulatory Capital Requirements Ratio | 4.00% | 4.00%
Leverage Ratio, To be Well Capitalized Amount | $ 298,551 | $ 237,369
Leverage Ratio, To be Well Capitalized Ratio | 5.00% | 5.00%
Tier One Common Equity Capital | $ 515,234 | $ 445,114
Tier One Common Equity Capital to Risk Weighted Assets | 9.77% | 11.81%
Tier One Common Equity Capital Required for Capital Adequacy | $ 237,315 | $ 169,621
Tier One Common Equity Capital Required for Capital Adequacy to Risk Weighted Assets | 4.50% | 4.50%
Tier One Common Equity Capital Required to be Well Capitalized | $ 342,788 | $ 245,008
Tier One Common Equity Capital Required to be Well Capitalized to Risk Weighted Assets | 6.50% | 6.50%
Tier 1 Capital (to Risk-Weighted Assets), Actual Amount | $ 535,234 | $ 465,114
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio | 10.15% | 12.34%
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 316,419 | $ 150,774
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 6.00% | 4.00%
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 421,892 | $ 226,161
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 8.00% | 6.00%
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 611,859 | $ 537,935
Total Capital (to Risk-Weighted Assets), Actual Ratio | 11.60% | 14.27%
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 421,892 | $ 301,548
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 8.00% | 8.00%
Total Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 527,366 | $ 376,936
Total Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 10.00% | 10.00%
S&T Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Leverage Ratio, Actual Amount | $ 502,114 | $ 403,593
Leverage Ratio, Actual Ratio | 8.43% | 8.53%
Leverage Ratio, Minimum Regulatory Capital Requirements Amount | $ 238,121 | $ 189,182
Leverage Ratio, Minimum Regulatory Capital Requirements Ratio | 4.00% | 4.00%
Leverage Ratio, To be Well Capitalized Amount | $ 297,651 | $ 236,477
Leverage Ratio, To be Well Capitalized Ratio | 5.00% | 5.00%
Tier One Common Equity Capital | $ 502,114 | $ 403,593
Tier One Common Equity Capital to Risk Weighted Assets | 9.55% | 10.76%
Tier One Common Equity Capital Required for Capital Adequacy | $ 236,482 | $ 168,804
Tier One Common Equity Capital Required for Capital Adequacy to Risk Weighted Assets | 4.50% | 4.50%
Tier One Common Equity Capital Required to be Well Capitalized | $ 341,584 | $ 243,827
Tier One Common Equity Capital Required to be Well Capitalized to Risk Weighted Assets | 6.50% | 6.50%
Tier 1 Capital (to Risk-Weighted Assets), Actual Amount | $ 502,114 | $ 403,593
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio | 9.55% | 10.76%
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 315,309 | $ 150,048
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 6.00% | 4.00%
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 420,412 | $ 225,071
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 8.00% | 6.00%
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 577,824 | $ 475,538
Total Capital (to Risk-Weighted Assets), Actual Ratio | 11.00% | 12.68%
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 420,412 | $ 300,095
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 8.00% | 8.00%
Total Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 525,515 | $ 375,119
Total Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 10.00% | 10.00%

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- Definition The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 + Details
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