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