EMPLOYEE BENEFITS (Asset Allocation) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 248,735	$ 199,466	$ 164,819
Actual % of total	100.00%	100.00%
Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 21,718	$ 13,250
Actual % of total	8.70%	6.70%
Fixed maturity securities - corporate bonds | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Fixed maturity securities - corporate bonds | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	15.00%
Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 3,534	$ 2,929
Actual % of total	1.40%	1.50%
Redeemable preferred stock | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Redeemable preferred stock | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 149,413	$ 117,117
Actual % of total	60.00%	58.70%
Equity securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	50.00%
Equity securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	70.00%
Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 26,266	$ 20,505
Actual % of total	10.60%	10.30%
Core plus bond separate account fund | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Core plus bond separate account fund | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	40.00%
U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 22,269	$ 22,114
Actual % of total	9.00%	11.10%
U.S. property separate account fund | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
U.S. property separate account fund | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	25.00%
Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 9,873	$ 9,245
Actual % of total	4.00%	4.60%
Arbitrage fund | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Arbitrage fund | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
United Life annuity
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 11,398	$ 10,855
Actual % of total	4.60%	5.40%
United Life annuity | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
United Life annuity | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 4,264	$ 3,451
Actual % of total	1.70%	1.70%
Cash and cash equivalents | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Cash and cash equivalents | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%