EMPLOYEE BENEFIT PLANS - Defined Benefit Plan Assets by Category (Details) - Qualified Plan - Qualified Pension Plan - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
EMPLOYEE BENEFIT PLANS
Total investments	$ 304,822	$ 253,955	$ 260,926
Employer contribution receivable	0	0
Total	304,822	253,955
Cash and cash equivalents
EMPLOYEE BENEFIT PLANS
Total investments	3,713	1,225
Collective Russell 3000 index fund
EMPLOYEE BENEFIT PLANS
Total investments	100,673	70,599
Fidelity Spartan 500 index fund
EMPLOYEE BENEFIT PLANS
Total investments	31,693	46,300
Northern Trust ACWI ex-US Fund
EMPLOYEE BENEFIT PLANS
Total investments	56,996	41,924
Group deposit administration annuity contract
EMPLOYEE BENEFIT PLANS
Total investments	75,052	78,707
BlackRock Long Government Credit Bond Index Fund
EMPLOYEE BENEFIT PLANS
Total investments	$ 36,695	$ 15,200