EMPLOYEE BENEFITS (Fair Value of Plan Assets) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	$ 157,644	$ 128,430	$ 106,600
Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	11,003	9,451
Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	3,216	3,144
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	87,603	69,770
Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	17,948	10,401
U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	15,502	14,330
U.S. property separate account fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	15,502	14,330	$ 11,252
Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	8,506	8,292
Recurring
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	147,789	119,047
Recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	94,830	76,573
Recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	37,457	28,144
Recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	15,502	14,330
Recurring | Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	11,003	9,451
Recurring | Fixed maturity securities - corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Fixed maturity securities - corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	11,003	9,451
Recurring | Fixed maturity securities - corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	3,216	3,144
Recurring | Redeemable preferred stock | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	3,216	3,144
Recurring | Redeemable preferred stock | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Redeemable preferred stock | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	87,603	69,770
Recurring | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	87,603	69,770
Recurring | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	17,948	10,401
Recurring | Core plus bond separate account fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Core plus bond separate account fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	17,948	10,401
Recurring | Core plus bond separate account fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	15,502	14,330
Recurring | U.S. property separate account fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | U.S. property separate account fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | U.S. property separate account fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	15,502	14,330
Recurring | Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	8,506	8,292
Recurring | Arbitrage fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Arbitrage fund | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	8,506	8,292
Recurring | Arbitrage fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,011	3,659
Recurring | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,011	3,659
Recurring | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Recurring | Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	$ 0	$ 0