EMPLOYEE BENEFIT PLANS - Level 3 Financial Instrument (Details) - Qualified Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Qualified Pension Plan
Employee benefit plans
Fair Value	$ 253,955	$ 260,926	$ 201,843
Qualified Pension Plan | Level 3
Employee benefit plans
Fair Value	78,707	74,886	$ 71,226
Group deposit administration annuity contract | Qualified Pension Plan
Employee benefit plans
Fair Value	78,707	74,886
Group deposit administration annuity contract | Qualified Pension Plan | Level 3
Employee benefit plans
Fair Value	$ 78,707	$ 74,886
Group deposit administration annuity contract | Level 3 | Contract Value | Minimum
Employee benefit plans
Contract rate (as a percent)	5.06%
Group deposit administration annuity contract | Level 3 | Contract Value | Maximum
Employee benefit plans
Contract rate (as a percent)	5.14%