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	58,001				58,001
Other comprehensive income (loss), net of tax	(60,081)						(60,081)
Cash dividends declared	(23,175)				(23,175)
Treasury stock issued for restricted stock awards	0				(135)			135
Forfeitures of restricted stock awards	(434)				1,294			(1,728)
Repurchase of S&T Stock	(4,153)							(4,153)
Recognition of restricted stock compensation expense	1,746			1,746
Ending Balance at Jun. 30, 2022	1,178,358		103,623	404,841	809,644		(67,171)	(72,579)
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 Mar. 31, 2022	$ 1,184,950		103,623	403,841	791,345		(47,043)	(66,816)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,858				28,858
Other comprehensive income (loss), net of tax	(20,128)						(20,128)
Cash dividends declared	(11,791)				(11,791)
Forfeitures of restricted stock awards	(378)				1,232			(1,610)
Repurchase of S&T Stock	(4,153)							(4,153)
Recognition of restricted stock compensation expense	1,000			1,000
Ending Balance at Jun. 30, 2022	1,178,358		103,623	404,841	809,644		(67,171)	(72,579)
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	74,266				74,266
Other comprehensive income (loss), net of tax	(1,918)						(1,918)
Cash dividends declared	(24,910)				(24,910)
Treasury stock issued for restricted stock awards	0			(997)				997
Forfeitures of restricted stock awards	(482)				1,117			(1,599)
Repurchase of S&T Stock	(19,998)							(19,998)
Recognition of restricted stock compensation expense	1,683			1,683
Ending Balance at Jun. 30, 2023	1,212,853		103,623	406,969	913,974		(114,043)	(97,670)
Beginning Balance at Mar. 31, 2023	1,227,795		103,623	407,113	890,840		(96,658)	(77,123)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,467				34,467
Other comprehensive income (loss), net of tax	(17,385)						(17,385)
Cash dividends declared	(12,416)				(12,416)
Treasury stock issued for restricted stock awards	0			(997)				997
Forfeitures of restricted stock awards	(463)				1,083			(1,546)
Repurchase of S&T Stock	(19,998)							(19,998)
Recognition of restricted stock compensation expense	853			853
Ending Balance at Jun. 30, 2023	$ 1,212,853		$ 103,623	$ 406,969	$ 913,974		$ (114,043)	$ (97,670)