REGULATORY MATTERS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Tier 1 Leverage ratio [Abstract]
Tier 1 Leverage ratio, actual amount	$ 1,148,336	$ 1,093,166
Tier 1 Leverage ratio, actual ratio	10.80%	11.08%
Tier 1 leverage ratio for capital adequacy purposes, amount	$ 425,431	$ 394,700
Tier 1 leverage ratio for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 leverage capital to be well-capitalized under prompt corrective action, amount	$ 531,788	$ 493,375
Tier 1 leverage capital to be well-capitalized under prompt corrective action, ratio	5.00%	5.00%
Tier 1 risk-based capital [Abstract]
Tier 1 risk-based capital, actual amount	$ 1,148,336	$ 1,093,166
Tier 1 risk-based capital, actual ratio	17.23%	18.23%
Tier 1 risk-based capital for capital adequacy purposes, amount	$ 399,834	$ 359,747
Tier 1 risk-based capital for capital adequacy purposes, ratio	6.00%	6.00%
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, amount	$ 566,432	$ 472,168
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, ratio	8.50%	7.875%
Tier 1 risk based capital to be well-capitalized under prompt corrective action, amount	$ 533,112	$ 479,662
Tier 1 risk-based capital to be well-capitalized under prompt corrective action, ratio	8.00%	8.00%
Total risk-based capital [Abstract]
Total risk-based capital, actual amount	$ 1,198,724	$ 1,142,927
Total risk-based capital, actual ratio	17.99%	19.06%
Total risk-based capital for capital adequacy purposes, amount	$ 533,112	$ 479,662
Total risk-based capita for capital adequacy purposes, ratio	8.00%	8.00%
Total risk-based capital for capital adequacy purposes plus capital conservation buffer, amount	$ 699,710	$ 592,083
Total risk-based capita for capital adequacy purposes plus capital conservation buffer, ratio	10.50%	9.875%
Total risk based capital to be well-capitalized under prompt corrective action, amount	$ 666,390	$ 599,578
Total risk based capital to be well-capitalized under prompt corrective action, ratio	10.00%	10.00%
Common equity Tier 1 capital [Abstract]
Common equity Tier 1 capital, actual amount	$ 1,073,281	$ 998,111
Common equity Tier 1 capital, actual ratio	16.11%	16.65%
Common equity Tier 1 capital for capital adequacy purposes, amount	$ 299,876	$ 269,810
Common equity Tier 1 capital for capital adequacy purposes, ratio	4.50%	4.50%
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, amount	$ 466,473	$ 382,231
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, ratio	7.00%	6.375%
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, amount	$ 433,154	$ 389,726
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, ratio	6.50%	6.50%
Community Bank, N.A. [Member]
Tier 1 Leverage ratio [Abstract]
Tier 1 Leverage ratio, actual amount	$ 910,364	$ 912,995
Tier 1 Leverage ratio, actual ratio	8.61%	9.32%
Tier 1 leverage ratio for capital adequacy purposes, amount	$ 422,882	$ 391,953
Tier 1 leverage ratio for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 leverage capital to be well-capitalized under prompt corrective action, amount	$ 528,603	$ 489,941
Tier 1 leverage capital to be well-capitalized under prompt corrective action, ratio	5.00%	5.00%
Tier 1 risk-based capital [Abstract]
Tier 1 risk-based capital, actual amount	$ 910,364	$ 912,995
Tier 1 risk-based capital, actual ratio	13.79%	15.35%
Tier 1 risk-based capital for capital adequacy purposes, amount	$ 396,064	$ 356,973
Tier 1 risk-based capital for capital adequacy purposes, ratio	6.00%	6.00%
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, amount	$ 561,091	$ 468,527
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, ratio	8.50%	7.875%
Tier 1 risk based capital to be well-capitalized under prompt corrective action, amount	$ 528,086	$ 475,964
Tier 1 risk-based capital to be well-capitalized under prompt corrective action, ratio	8.00%	8.00%
Total risk-based capital [Abstract]
Total risk-based capital, actual amount	$ 960,752	$ 962,756
Total risk-based capital, actual ratio	14.55%	16.18%
Total risk-based capital for capital adequacy purposes, amount	$ 528,086	$ 475,964
Total risk-based capita for capital adequacy purposes, ratio	8.00%	8.00%
Total risk-based capital for capital adequacy purposes plus capital conservation buffer, amount	$ 693,113	$ 587,518
Total risk-based capita for capital adequacy purposes plus capital conservation buffer, ratio	10.50%	9.875%
Total risk based capital to be well-capitalized under prompt corrective action, amount	$ 660,107	$ 594,955
Total risk based capital to be well-capitalized under prompt corrective action, ratio	10.00%	10.00%
Common equity Tier 1 capital [Abstract]
Common equity Tier 1 capital, actual amount	$ 910,309	$ 912,940
Common equity Tier 1 capital, actual ratio	13.79%	15.35%
Common equity Tier 1 capital for capital adequacy purposes, amount	$ 297,048	$ 267,730
Common equity Tier 1 capital for capital adequacy purposes, ratio	4.50%	4.50%
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, amount	$ 462,075	$ 379,284
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, ratio	7.00%	6.375%
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, amount	$ 429,070	$ 386,721
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, ratio	6.50%	6.50%