EMPLOYEE BENEFIT PLANS - Schedule of Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 94,962	$ 83,086	$ 73,619
UK Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	94,961	83,086
UK Pension Plan | Quoted Prices in Active Markets for Identical Items (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	15,600	10,579
UK Pension Plan | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	79,361	72,507
UK Pension Plan | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	15,600	10,579
UK Pension Plan | Cash | Quoted Prices in Active Markets for Identical Items (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	15,600	10,579
UK Pension Plan | Diversified Growth Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	22,640	20,102
UK Pension Plan | Diversified Growth Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	22,640	20,102
UK Pension Plan | Global Equity Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	2,922	3,207
UK Pension Plan | Global Equity Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	2,922	3,207
UK Pension Plan | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	17,478	16,166
UK Pension Plan | Fixed Income Securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	17,478	16,166
UK Pension Plan | Government Index Linked Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	15,331	13,012
UK Pension Plan | Government Index Linked Securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	15,331	13,012
UK Pension Plan | Global Absolute Return Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	12,235	11,871
UK Pension Plan | Global Absolute Return Bond Fund | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	12,235	11,871
UK Pension Plan | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	8,755	8,149
UK Pension Plan | Corporate Bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 8,755	$ 8,149