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Basis of Presentation (Details) $ / shares in Units, $ in Thousands | Jun. 05, 2019 branch $ / shares shares | Jun. 30, 2019 USD ($) lease $ / shares | Mar. 31, 2019 USD ($) | Jan. 01, 2019 USD ($) lease | Dec. 31, 2018 $ / shares | Jan. 01, 2018
--- | --- | --- | --- | --- | --- | ---
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  | $ 2.50 |  |  | $ 2.50 |
Lease Liabilities |  | $ 1,234 |  |  |  |
Operating lease, liabilities |  | 41,062 |  |  |  |
Financing lease, right-of-use assets |  | 1,191 |  |  |  |
Operating lease, right-of-use assets |  | $ 36,417 |  |  |  |
Number of operating lease agreements | lease |  | 42 |  |  |  |
ASU No. 2016-02 |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Lease Liabilities |  |  |  | $ 1,200 |  |
Operating lease, liabilities |  |  |  | 33,700 |  |
Financing lease, right-of-use assets |  |  |  | 1,200 |  |
Operating lease, right-of-use assets |  |  |  | $ 33,400 |  |
Number of operating lease agreements | lease |  |  |  | 1 |  |
New Partnership |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Equity method investment, ownership percentage |  |  |  |  |  | 30.00%
S&T Evergreen Insurance LLC | Subsidiaries |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Percentage of ownership in subsidiary sold |  |  |  |  |  | 70.00%
DNB |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Number of branches | branch | 14 |  |  |  |  |
Total assets of DNB |  |  | $ 1,200,000 |  |  |
Shares of S&T offered for each share of DNB (shares) | shares | 1.22 |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares | $ 2.50 |  |  |  |  |
DNB | DNB |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares | $ 1.00 |  |  |  |  |

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