REGULATORY MATTERS (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Tier 1 Leverage ratio [Abstract]
Required capital conservation ratio	2.50%
Tier 1 Leverage ratio, actual amount	$ 1,314,864	$ 1,148,336
Tier 1 Leverage ratio, actual ratio	10.16	10.80
Tier 1 leverage ratio for capital adequacy purposes, amount	$ 517,736	$ 425,431
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	$ 647,169	$ 531,788
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	$ 1,314,864	$ 1,148,336
Tier 1 risk-based capital, actual ratio	18.99	17.23
Tier 1 risk-based capital for capital adequacy purposes, amount	$ 415,472	$ 399,834
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	$ 588,585	$ 566,432
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, ratio	8.50%	8.50%
Tier 1 risk based capital to be well-capitalized under prompt corrective action, amount	$ 553,962	$ 533,112
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	$ 1,375,704	$ 1,198,724
Total risk-based capital, actual ratio	19.87	17.99
Total risk-based capital for capital adequacy purposes, amount	$ 553,962	$ 533,112
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	$ 727,075	$ 699,710
Total risk-based capita for capital adequacy purposes plus capital conservation buffer, ratio	10.50%	10.50%
Total risk based capital to be well-capitalized under prompt corrective action, amount	$ 692,453	$ 666,390
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	$ 1,239,754	$ 1,073,281
Common equity Tier 1 capital, actual ratio	17.90	16.11
Common equity Tier 1 capital for capital adequacy purposes, amount	$ 311,604	$ 299,876
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	$ 484,717	$ 466,473
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, ratio	7.00%	7.00%
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, amount	$ 450,094	$ 433,154
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	$ 1,028,285	$ 910,364
Tier 1 Leverage ratio, actual ratio	7.98	8.61
Tier 1 leverage ratio for capital adequacy purposes, amount	$ 515,552	$ 422,882
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	$ 644,440	$ 528,603
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	$ 1,028,285	$ 910,364
Tier 1 risk-based capital, actual ratio	14.98	13.79
Tier 1 risk-based capital for capital adequacy purposes, amount	$ 411,880	$ 396,064
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	$ 583,497	$ 561,091
Tier 1 risk-based capital for capital adequacy purposes plus capital conservation buffer, ratio	8.50%	8.50%
Tier 1 risk based capital to be well-capitalized under prompt corrective action, amount	$ 549,174	$ 528,086
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	$ 1,089,125	$ 960,752
Total risk-based capital, actual ratio	15.87	14.55
Total risk-based capital for capital adequacy purposes, amount	$ 549,174	$ 528,086
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	$ 720,791	$ 693,113
Total risk-based capita for capital adequacy purposes plus capital conservation buffer, ratio	10.50%	10.50%
Total risk based capital to be well-capitalized under prompt corrective action, amount	$ 686,467	$ 660,107
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	$ 1,028,175	$ 910,309
Common equity Tier 1 capital, actual ratio	14.98	13.79
Common equity Tier 1 capital for capital adequacy purposes, amount	$ 308,910	$ 297,048
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	$ 480,527	$ 462,075
Common equity Tier 1 capital for capital adequacy purposes plus capital conservation buffer, ratio	7.00%	7.00%
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, amount	$ 446,204	$ 429,070
Common equity Tier 1 capital to be well-capitalized under prompt corrective action, ratio	6.50%	6.50%