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v3.20.4

Business Combinations - Additional Information (Details) |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) | Nov. 30, 2020 USD ($) | Dec. 31, 2019 USD ($) | Nov. 30, 2019 USD ($) banking_location $ / shares shares | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |
Goodwill | $ 373,424,000 |  | $ 371,621,000 |  | $ 373,424,000 | $ 371,621,000 |
Adjustments, loans | 8,600,000 |  | $ 12,300,000 |  |  |  |
Merger related expenses |  |  |  |  | 2,342,000 | 11,350,000 | $ 0
Professional services and legal |  |  |  |  | 6,394,000 | 4,244,000 | $ 4,132,000
DNB |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Number of banking locations | banking_location |  |  |  | 14 |  |  |
Shares of S&T offered for each share of DNB (in shares) | shares |  |  |  | 1.22 |  |  |
Fair value of total consideration |  | $ 200,991,000 |  | $ 200,991,000 |  |  |
Cash |  | 360,000 |  | $ 360,000 |  |  |
S&T common shares issued (in shares) | shares |  |  |  | 5,318,964 |  |  |
S&T common shares issued, fair value (in USD per share) | $ / shares |  |  |  | $ 37.72 |  |  |
Goodwill | 86,000,000.0 | 85,978,000 |  | $ 84,175,000 | 86,000,000.0 |  |
Preliminary estimates adjustments |  | 1,803,000 |  |  |  |  |
Adjustments, loans |  | 2,377,000 |  | 8,143,000 |  |  |
Adjustments, borrowings |  | 257,000 |  | 276,000 |  |  |
Adjustment, other liabilities |  | 122,000 |  | 3,184,000 |  |  |
Adjustments, other assets |  | 116,000 |  | 4,278,000 |  |  |
Adjustments, deferred income taxes |  | 311,000 |  | (3,298,000) |  |  |
Carryover of allowance for credit losses |  | 0 |  | 0 |  |  |
Fair value of loans acquired |  | $ 906,607,000 |  | 908,984,000 |  |  |
Discount on loans acquired |  |  |  | $ 10,500,000 |  |  |
Direct costs related to merger | $ 13,700,000 |  |  |  | 13,700,000 |  |
Merger related expenses |  |  |  |  | 2,300,000 | 11,400,000 |
Professional services and legal |  |  |  |  | 200,000 | 2,800,000 |
Severance payments |  |  |  |  | 1,400,000 | 3,400,000 |
Data processing, contract termination and conversion cost expenses |  |  |  |  | 400,000 | 4,700,000 |
Other expenses |  |  |  |  | $ 300,000 | $ 500,000 |

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