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, 2022	$ 1,184,659	$ (447)	$ 103,623	$ 406,283	$ 863,948	$ (447)	$ (112,125)	$ (77,070)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	107,734				107,734
Other comprehensive income (loss), net of tax	(13,511)						(13,511)
Cash dividends declared	(37,190)				(37,190)
Treasury stock issued for restricted stock awards	0			(1,113)				1,113
Forfeitures of restricted stock awards	(521)				1,117			(1,638)
Repurchase of S&T Stock	(19,998)							(19,998)
Recognition of restricted stock compensation expense	2,806			2,806
Balance at end of period at Sep. 30, 2023	1,223,532		103,623	407,976	935,162		(125,636)	(97,593)
Balance at beginning of period at Jun. 30, 2023	1,212,853		103,623	406,969	913,974		(114,043)	(97,670)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,468				33,468
Other comprehensive income (loss), net of tax	(11,593)						(11,593)
Cash dividends declared	(12,280)				(12,280)
Treasury stock issued for restricted stock awards	0			(116)				116
Forfeitures of restricted stock awards	(39)							(39)
Recognition of restricted stock compensation expense	1,123			1,123
Balance at end of period at Sep. 30, 2023	1,223,532		103,623	407,976	935,162		(125,636)	(97,593)
Balance at beginning of period at Dec. 31, 2023	1,283,445	$ (1,002)	103,623	409,034	959,604	$ (1,002)	(90,901)	(97,915)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,200				98,200
Other comprehensive income (loss), net of tax	30,393						30,393
Cash dividends declared	(38,012)				(38,012)
Treasury stock issued for restricted stock awards	0			(1,861)				1,861
Forfeitures of restricted stock awards	(849)				243			(1,092)
Recognition of restricted stock compensation expense	3,579			3,579
Balance at end of period at Sep. 30, 2024	1,375,754		103,623	410,752	1,019,033		(60,508)	(97,146)
Balance at beginning of period at Jun. 30, 2024	1,321,443		103,623	409,874	999,115		(93,934)	(97,235)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,590				32,590
Other comprehensive income (loss), net of tax	33,426						33,426
Cash dividends declared	(12,679)				(12,679)
Treasury stock issued for restricted stock awards	0			(164)				164
Forfeitures of restricted stock awards	(68)				7			(75)
Recognition of restricted stock compensation expense	1,042			1,042
Balance at end of period at Sep. 30, 2024	$ 1,375,754		$ 103,623	$ 410,752	$ 1,019,033		$ (60,508)	$ (97,146)