CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss	Treasury Stock
Balance at beginning of period at Dec. 31, 2020	$ 1,154,711		$ 103,623	$ 400,668	$ 710,061		$ 8,971	$ (68,612)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	110,343				110,343
Other comprehensive income (loss), net of tax	(16,061)						(16,061)
Cash dividends declared	(44,336)				(44,336)
Treasury stock issued for restricted stock awards	0				(4,163)			4,163
Forfeitures of restricted stock awards	(630)				1,754			(2,384)
Recognition of restricted stock compensation expense	2,427			2,427
Balance at end of period at Dec. 31, 2021	1,206,454		103,623	403,095	773,659		(7,090)	(66,833)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	135,520				135,520
Other comprehensive income (loss), net of tax	(105,035)						(105,035)
Cash dividends declared	(47,023)				(47,023)
Treasury stock issued for restricted stock awards	0				(135)			135
Forfeitures of restricted stock awards	(808)				1,927			(2,735)
Repurchase of S&T Stock	(7,637)							(7,637)
Recognition of restricted stock compensation expense	3,188			3,188
Balance at end of period at Dec. 31, 2022	$ 1,184,659	$ (447)	103,623	406,283	863,948	$ (447)	(112,125)	(77,070)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	Accounting Standards Update 2022-02
Net income	$ 144,781				144,781
Other comprehensive income (loss), net of tax	21,224						21,224
Cash dividends declared	(49,850)				(49,850)
Treasury stock issued for restricted stock awards	0			(1,123)				1,123
Forfeitures of restricted stock awards	(798)				1,172			(1,970)
Repurchase of S&T Stock	(19,998)							(19,998)
Recognition of restricted stock compensation expense	3,874			3,874
Balance at end of period at Dec. 31, 2023	$ 1,283,445		$ 103,623	$ 409,034	$ 959,604		$ (90,901)	$ (97,915)