EMPLOYEE BENEFITS (Fair Value of Plan Assets) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	$ 248,735	$ 199,466	$ 164,819
Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	21,718	13,250
Redeemable preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	3,534	2,929
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	149,413	117,117
Core plus bond separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	26,266	20,505
U.S. property separate account fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	22,269	22,114
U.S. property separate account fund | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	22,269	22,114	$ 20,841
Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	9,873	9,245
United Life annuity
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	11,398	10,855
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,264	3,451
Recurring
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	237,333	188,608
Recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	157,207	123,494
Recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	57,857	43,000
Recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	22,269	22,114
Recurring | Fixed maturity securities - corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	21,718	13,250
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	21,718	13,250
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	3,534	2,929
Recurring | Redeemable preferred stock | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	3,534	2,929
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	149,413	117,117
Recurring | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	149,413	117,117
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	26,266	20,505
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	26,266	20,505
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	22,269	22,114
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	22,269	22,114
Recurring | Arbitrage fund
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	9,873	9,245
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	9,873	9,245
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	4,260	3,448
Recurring | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,260	3,448
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