ACQUISITION OF FNB (Details) $ / shares in Units, shares in Thousands, $ in Thousands			12 Months Ended
		Dec. 11, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2015 Branches $ / shares
Adjustments to reflect liabilities acquired at fair value: [Abstract]
Goodwill resulting from merger	[1]		$ 21,089	$ 21,089
Merger and acquisition			0	1,103	$ 237
Assets (liabilities) acquired [Abstract]
Goodwill resulting from the FNB merger	[1]		21,089	21,089
First National Bank of Fredericksburg [Member]
Summarizes the purchase of FNB [Abstract]
Merger agreement per share in cash and stock (in dollars per share) | $ / shares						$ 630
Ownership percentage						100.00%
Business acquisition credit impaired loans purchased		$ 3,809
Purchase Price Consideration - Cash for Common Stock [Abstract]
Purchase price assigned to The First National Bank of Fredericksburg common shares exchanged for cash		5,619
Total Purchase Price		21,603
Net Assets Acquired [Abstract]
The First National Bank of Fredericksburg shareholders' equity		12,298
Loans [Abstract]
Interest rate		31
General credit		(1,362)
Specific credit - non-amortizing		(2,495)
Specific credit - amortizing		(665)
Core deposit intangible		1,641
Covenant not to compete		125
Premises and equipment		1,203
Leased premises contracts		(359)
Other assets		(358)
Deferred tax assets		785
Adjustments to reflect liabilities acquired at fair value: [Abstract]
Time deposits		(74)
Acquired and liabilities assumed, net		10,770
Goodwill resulting from merger		10,833	0	10,833	0
Goodwill and other intangibles		12,814
Merger and acquisition				1,103
Asset acquired and liability assumed [Abstract]
Total Purchase Price		21,603
Assets (liabilities) acquired [Abstract]
Cash and cash equivalents		83,514	0	83,514	0
Interest bearing time deposits with other banks		1,236	0	1,236	0
Securities available for sale		23,831	0	23,831	0
Loans		115,211	0	115,211	0
Premises and equipment, net		4,743	0	4,743	0
Accrued interest receivable		282	0	282	0
Bank-owned life insurance		4,598	0	4,598	0
Intangibles		1,981	0	1,981	0
Deferred tax asset		2,979	0	2,979	0
Other assets		2,332	0	2,332	0
Time deposits		(42,675)
Deposits other than time deposits		(182,555)
Accrued interest payable		(14)	0	(14)	0
Other liabilities		(4,693)	0	(4,693)	0
Acquired and liabilities assumed, net		10,770
Goodwill resulting from the FNB merger		$ 10,833	$ 0	$ 10,833	$ 0
First National Bank of Fredericksburg [Member] | Lebanon County [Member]
Summarizes the purchase of FNB [Abstract]
Number of Branches | Branches						4
First National Bank of Fredericksburg [Member] | Schuylkill County [Member]
Summarizes the purchase of FNB [Abstract]
Number of Branches | Branches						2
First National Bank of Fredericksburg [Member] | Berks County [Member]
Summarizes the purchase of FNB [Abstract]
Number of Branches | Branches						1
First National Bank of Fredericksburg [Member] | Common Stock [Member]
Purchase Price Consideration in Common Stock [Abstract]
Citizens Financial Services, Inc. shares issued (in shares) | shares		336,515
Value assigned to Citizens Financial Services, Inc. common share (in dollars per share) | $ / shares		$ 47.5
Purchase price assigned to FNB common shares exchanged for Citizens Financial Services, Inc.		$ 15,984

[1] Excludes fully amortized intangible assets