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Basis of Presentation (Details) - USD ($) $ in Thousands |  | 3 Months Ended
--- | --- | ---
Jan. 01, 2018 | Mar. 31, 2018 | Mar. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |
Gain on sale of a majority interest of insurance business |  |  | $ 1,873 | $ 0
Unrealized Gains/losses Recognized on Equity Securities Still Held |  |  | 52 | $ 363
Provisional estimate for reclassification of AOCI to retain earnings for other income tax effects of Tax Act |  |  | $ 3,700 |
Accounting Standards Update 2016-01 | AOCI |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Reclassification of net unrealized gains on equity securities | [1] | $ (862) |  |
Accounting Standards Update 2016-01 | Retained Earnings |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Reclassification of net unrealized gains on equity securities | [1] | $ 862 |  |
New Partnership |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity method investment, ownership percentage |  | 30.00% |  |
Subsidiaries | S&T Evergreen Insurance LLC |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Percentage of ownership in subsidiary sold |  | 70.00% |  |
Gain on sale of a majority interest of insurance business |  | $ 1,900 |  |
[1] | Reclassification due to the adoption of ASU No. 2016-01

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