EMPLOYEE BENEFITS (Asset Allocation) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 157,644	$ 128,430	$ 106,600
Actual % of total	100.00%	100.00%
Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 11,003	$ 9,451
Actual % of total	7.00%	7.40%
Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 3,216	$ 3,144
Actual % of total	2.00%	2.40%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 87,603	$ 69,770
Actual % of total	55.60%	54.30%
Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 17,948	$ 10,401
Actual % of total	11.40%	8.10%
U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 15,502	$ 14,330
Actual % of total	9.80%	11.10%
Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 8,506	$ 8,292
Actual % of total	5.40%	6.50%
United Life annuity
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 9,846	$ 9,377
Actual % of total	6.20%	7.30%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 4,020	$ 3,665
Actual % of total	2.60%	2.90%
Minimum | Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	50.00%
Minimum | Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | United Life annuity
Defined Benefit Plan Disclosure [Line Items]
Target allocation	5.00%
Minimum | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Maximum | Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation	15.00%
Maximum | Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
Maximum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	70.00%
Maximum | Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	40.00%
Maximum | U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	25.00%
Maximum | Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
Maximum | United Life annuity
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%
Maximum | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target allocation	10.00%