MERGER - Narrative (Details) $ / shares in Units, $ in Thousands		9 Months Ended	12 Months Ended
	Jul. 01, 2024 USD ($) $ / shares shares	Sep. 30, 2025 USD ($) $ / shares	Dec. 31, 2024 USD ($) $ / shares	Jun. 28, 2024 $ / shares	Dec. 31, 2023 USD ($)
Business Combination [Line Items]
Common stock, stated value (in usd per share) | $ / shares		$ 0.05205	$ 0.05205
Goodwill		$ 69,751	$ 68,106		$ 18,724
Adjustments to acquired goodwill		1,645	$ 0
Codorus Valley
Business Combination [Line Items]
Consideration transferred	$ 233,400
Goodwill	$ 49,400	51,000
Adjustments to acquired goodwill		$ 1,600
Estimated useful life (in years)	40 years
Operating lease assets acquired	$ 5,100
Operating lease liabilities acquired	5,100
Finance lease asset acquired	392
Finance lease liability acquired	392
Fair value adjustments of operating lease assets	(1,100)
Fair value adjustments of finance lease assets	(133)
Adjustments to deposits	3,200
Codorus Valley | Subordinated notes
Business Combination [Line Items]
Unamortized discount	2,400
Codorus Valley | Junior Subordinated Debt
Business Combination [Line Items]
Unamortized discount	2,700
Codorus Valley | Premises and Equipment
Business Combination [Line Items]
Adjustment to premises and equipment	6,600
Codorus Valley | Core deposit intangible
Business Combination [Line Items]
Other intangible assets, net	40,100
Codorus Valley | Customer relationship
Business Combination [Line Items]
Other intangible assets, net	$ 10,600
Expected life (in years)	10 years
Common Stock | Codorus Valley
Business Combination [Line Items]
Business combination, shares of common stock to be received by acquiree for number of shares outstanding ratio	0.875
Codorus Valley | Common Stock | Codorus Valley
Business Combination [Line Items]
Common stock, stated value (in usd per share) | $ / shares	$ 2.50
Orrstown Financial Services Inc | Codorus Valley
Business Combination [Line Items]
Shares issued for common stock (in shares) | shares	8,532,038
Share price (in usd per share) | $ / shares				$ 27.36