ACQUISITION OF HV BANCORP, INC, Summary of Purchase of HVB Acquisition (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 16, 2023	Dec. 31, 2023	Dec. 31, 2022	Apr. 17, 2020
Fair Value of Liabilities Assumed [Abstract]
Goodwill		$ 85,758	$ 31,376
HV Bancorp, Inc. [Member]
Purchase Price Consideration in Common Stock [Abstract]
Citizens Financial Services, Inc. shares issued (in shares)	693,858
Value assigned to Citizens Financial Services, Inc. common share (in dollars per share)	$ 86.67
Purchase price assigned to HVBC common shares exchanged for Citizens Financial Services, Inc.	$ 60,137
Purchase Price Consideration - Cash for Common Stock [Abstract]
Purchase price assigned to HVBC's common shares exchanged for cash	13,112
Purchase Price Related to Cash Payout of Stock Options	3,416
Total Purchase Price	76,665
Net Assets Acquired [Abstract]
HV Bancorp, Inc shareholders' equity	40,630
Adjustments to Reflect Assets Acquired at Fair Value [Abstract]
Investments	31
Loans [Abstract]
Interest rate	(24,097)
General credit	(1,834)
Specific credit - PCD accrual	(277)
Specific credit - PCD non-accrual	(1,765)
Core deposit intangible	2,770
Owned premises	67
Other assets	(193)
Deferred tax assets	3,051
Fair Value of Liabilities Assumed [Abstract]
Time deposits	586
Borrowings	3,017
Other liabilities	297
Total fair value of identifiable net assets	22,283
Goodwill	$ 54,382	$ 54,382	$ 0	$ 0