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Allowance for Credit Losses - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2020 | Jan. 01, 2020 | Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Adjustment to allowance for credit loss | $ 96,850 | $ 62,224 | $ 62,224
ACL provision, COVID-19 assessment | 14,900 |  |
ACL provision, COVID-19 assessment, revised forecast | 11,200 |  |
ACL provision, COVID-19 assessment, changes in current conditions | $ 3,700 |  |
Impact of ASU 2016-13 Adoption |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Adjustment to allowance for credit loss |  | 27,353 | $ 27,352
S&T Legacy Loans | Impact of ASU 2016-13 Adoption |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Adjustment to allowance for credit loss |  | 8,200 |
Commercial and industrial | Impact of ASU 2016-13 Adoption |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Adjustment to allowance for credit loss |  | 9,900 |
DNB | Impact of ASU 2016-13 Adoption |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Adjustment to allowance for credit loss |  | $ 9,300 |

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