REGULATORY CAPITAL REQUIREMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Company (consolidated) [Member]
Total capital (to risk weighted assets):
Actual	$ 886,807	$ 824,265
Actual Ratio	13.82%	13.60%
Capital Required for Capital Adequacy	$ 513,398	$ 484,942
For Capital Adequacy Purposes Ratio	8.00%	8.00%
Common Equity Tier One Capital	$ 718,995	$ 656,080
Common Equity tier One Capital to Risk Weighted Assets	11.20%	10.82%
Common Equity Tier One Capital Required for Capital Adequacy	$ 288,787	$ 272,780
Common Equity Tier One Capital for Capitalized Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier 1 capital (to risk weighted assets):
Actual	$ 789,992	$ 727,070
Actual Ratio	12.31%	11.99%
For Capital Adequacy Purposes	$ 385,049	$ 363,706
For Capital Adequacy Purposes Ratio	6.00%	6.00%
Tier 1 capital (to average assets):
Actual	$ 789,992	$ 727,070
Actual Ratio	10.04%	9.77%
For Capital Adequacy Purposes	$ 314,756	$ 297,748
For Capital Adequacy Purposes Ratio	4.00%	4.00%
Bank [Member]
Total capital (to risk weighted assets):
Actual	$ 846,147	$ 788,320
Actual Ratio	13.19%	13.01%
Capital Required for Capital Adequacy	$ 513,175	$ 484,834
For Capital Adequacy Purposes Ratio	8.00%	8.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 641,469	$ 606,042
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	10.00%	10.00%
Common Equity Tier One Capital	$ 784,014	$ 725,760
Common Equity tier One Capital to Risk Weighted Assets	12.22%	11.98%
Common Equity Tier One Capital Required for Capital Adequacy	$ 288,661	$ 272,719
Common Equity Tier One Capital for Capitalized Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier 1 Capital to be Well Capitalized	$ 416,955	$ 393,927
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier 1 capital (to risk weighted assets):
Actual	$ 784,014	$ 725,760
Actual Ratio	12.22%	11.98%
For Capital Adequacy Purposes	$ 384,881	$ 363,625
For Capital Adequacy Purposes Ratio	6.00%	6.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 513,175	$ 484,834
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	8.00%	8.00%
Tier 1 capital (to average assets):
Actual	$ 784,014	$ 725,760
Actual Ratio	9.97%	9.76%
For Capital Adequacy Purposes	$ 314,630	$ 297,589
For Capital Adequacy Purposes Ratio	4.00%	4.00%
To Be Well Capitalized Under Prompt Correction Action Provisions	$ 393,288	$ 371,986
To Be Well Capitalized Under Prompt Correction Action Provisions Ratio	5.00%	5.00%