REGULATORY MATTERS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Total core capital to risk-weighted assets [Abstract]
Minimum total core capital to risk-weighted assets for capital adequacy (in hundredths)	8.00%
Minimum Tier I capital to risk-weighted assets for capital adequacy (in hundredths)	4.00%
Minimum Tier I capital to average assets for capital adequacy (in hundredths)	4.00%
Minimum total core capital to risk-weighted assets to be well capitalized (in hundredths)	10.00%
Minimum Tier I capital to risk-weighted assets to be well capitalized (in hundredths)	6.00%
Minimum Tier I capital to average assets to be well capitalized (in hundredths)	5.00%
Community Bank System, Inc [Member]
Tier 1 capital to average assets [Abstract]
Tier 1 Capital	$ 643,286	$ 588,220
Tier 1 capital to average assets (in hundredths)	9.29%	8.40%
Minimum required amount	276,918	280,151
Tier 1 capital to risk-weighted assets [Abstract]
Tier 1 Capital	643,286	588,220
Tier 1 capital to risk-weighted assets (in hundredths)	16.42%	15.09%
Minimum required amount	156,661	155,904
Total core capital to risk-weighted assets [Abstract]
Core Capital	687,946	631,409
Total core capital to risk-weighted assets (in hundredths)	17.57%	16.20%
Minimum required amount	313,322	311,808
Community Bank, N.A. [Member]
Tier 1 capital to average assets [Abstract]
Tier 1 Capital	547,464	530,753
Tier 1 capital to average assets (in hundredths)	7.93%	7.60%
Minimum required amount	276,226	279,524
Tier 1 capital to risk-weighted assets [Abstract]
Tier 1 Capital	547,464	530,753
Tier 1 capital to risk-weighted assets (in hundredths)	14.03%	13.66%
Minimum required amount	156,083	155,392
Total core capital to risk-weighted assets [Abstract]
Core Capital	592,124	573,942
Total core capital to risk-weighted assets (in hundredths)	15.17%	14.77%
Minimum required amount	$ 312,166	$ 310,784