CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Impact of adopting ASU 2022-02	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Impact of adopting ASU 2022-02	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance 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	95,250				95,250
Other comprehensive income (loss), net of tax	(107,877)						(107,877)
Cash dividends declared	(34,922)				(34,922)
Treasury stock issued for restricted stock awards	0				(135)			135
Forfeitures of restricted stock awards	(498)				1,832			(2,330)
Repurchase of S&T Stock	(7,637)							(7,637)
Recognition of restricted stock compensation expense	2,411			2,411
Ending Balance at Sep. 30, 2022	1,153,181		103,623	405,506	835,684		(114,967)	(76,665)
Beginning Balance at Dec. 31, 2021	1,206,454		103,623	403,095	773,659		(7,090)	(66,833)
Ending Balance 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
Beginning Balance at Jun. 30, 2022	$ 1,178,358		103,623	404,841	809,644		(67,171)	(72,579)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,249				37,249
Other comprehensive income (loss), net of tax	(47,796)						(47,796)
Cash dividends declared	(11,747)				(11,747)
Forfeitures of restricted stock awards	(64)				538			(602)
Repurchase of S&T Stock	(3,484)							(3,484)
Recognition of restricted stock compensation expense	665			665
Ending Balance at Sep. 30, 2022	1,153,181		103,623	405,506	835,684		(114,967)	(76,665)
Beginning Balance 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
Ending Balance at Sep. 30, 2023	1,223,532		103,623	407,976	935,162		(125,636)	(97,593)
Beginning Balance 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
Ending Balance at Sep. 30, 2023	$ 1,223,532		$ 103,623	$ 407,976	$ 935,162		$ (125,636)	$ (97,593)