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Regulatory Matters - Summary of Risk-Based Capital Amounts and Ratios for S&T and S&T Bank (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
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S&T |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Leverage Ratio, Actual Amount | $ 582,155 | $ 535,234
Leverage Ratio, Actual Ratio | 8.98% | 8.96%
Leverage Ratio, Minimum Regulatory Capital Requirements Amount | $ 259,170 | $ 238,841
Leverage Ratio, Minimum Regulatory Capital Requirements Ratio | 4.00% | 4.00%
Leverage Ratio, To be Well Capitalized Amount | $ 323,963 | $ 298,551
Leverage Ratio, To be Well Capitalized Ratio | 5.00% | 5.00%
Tier One Common Equity Capital | $ 562,155 | $ 515,234
Tier One Common Equity Capital to Risk Weighted Assets | 10.04% | 9.77%
Tier One Common Equity Capital Required for Capital Adequacy | $ 252,079 | $ 237,315
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 | $ 364,114 | $ 342,788
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 | $ 582,155 | $ 535,234
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio | 10.39% | 10.15%
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 336,105 | $ 316,419
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 6.00% | 6.00%
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 448,140 | $ 421,892
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 8.00% | 8.00%
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 664,184 | $ 611,859
Total Capital (to Risk-Weighted Assets), Actual Ratio | 11.86% | 11.60%
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 448,140 | $ 421,892
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 | $ 560,175 | $ 527,366
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 | $ 542,048 | $ 502,114
Leverage Ratio, Actual Ratio | 8.39% | 8.43%
Leverage Ratio, Minimum Regulatory Capital Requirements Amount | $ 258,460 | $ 238,121
Leverage Ratio, Minimum Regulatory Capital Requirements Ratio | 4.00% | 4.00%
Leverage Ratio, To be Well Capitalized Amount | $ 323,075 | $ 297,651
Leverage Ratio, To be Well Capitalized Ratio | 5.00% | 5.00%
Tier One Common Equity Capital | $ 542,048 | $ 502,114
Tier One Common Equity Capital to Risk Weighted Assets | 9.71% | 9.55%
Tier One Common Equity Capital Required for Capital Adequacy | $ 251,213 | $ 236,482
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 | $ 362,864 | $ 341,584
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 | $ 542,048 | $ 502,114
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio | 9.71% | 9.55%
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 334,951 | $ 315,309
Tier 1 Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Ratio | 6.00% | 6.00%
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Amount | $ 446,601 | $ 420,412
Tier 1 Capital (to Risk-Weighted Assets), To be Well Capitalized Ratio | 8.00% | 8.00%
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 622,469 | $ 577,824
Total Capital (to Risk-Weighted Assets), Actual Ratio | 11.15% | 11.00%
Total Capital (to Risk-Weighted Assets), Minimum Regulatory Capital Requirements Amount | $ 446,602 | $ 420,412
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 | $ 558,252 | $ 525,515
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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