Parent Company Condensed Financial Information - Statements of Net Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Condensed Income Statements, Captions [Line Items]
Total Interest and Dividend Income	$ 516,490	$ 515,872	$ 477,901
Interest expense on long-term debt	1,932	1,964	1,332
Income Tax Expense (Benefit)	33,710	33,553	34,023
Equity in undistributed net income of:
Net Income	134,230	131,265	144,781
S&T
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiaries	65,536	66,775	86,950
Total Interest and Dividend Income	65,536	66,775	86,950
Interest expense on long-term debt	1,939	2,180	2,372
Other expenses	5,382	4,973	4,764
Total expense	7,321	7,153	7,136
Income before income tax and undistributed net income of subsidiaries	58,215	59,622	79,814
Income Tax Expense (Benefit)	(1,550)	(1,309)	(1,478)
Income before undistributed net income of subsidiaries	59,765	60,931	81,292
Equity in undistributed net income of:
Bank subsidiary	74,172	70,823	63,337
Nonbank subsidiaries	293	(489)	152
Net Income	$ 134,230	$ 131,265	$ 144,781