EMPLOYEE BENEFIT PLANS - Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Postretirement Medical Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 1,076	$ 1,174
Initial adoption of new plan	0	0
Service cost with interest to end of year	68	63	$ 78
Interest cost	26	39	44
Participant contributions	23	35
Benefits paid	(27)	(162)
Actuarial gain	208	(73)
Benefit obligation at end of year	1,374	1,076	1,174
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Employer (reimbursement)/contributions	4	127
Participant contributions	23	35
Benefits paid	(27)	(162)
Fair value of plan assets at end of year	0	0	0
Pension Plan | Chemogas Defined Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	1,738	0
Acquisitions	0	1,738
Service cost with interest to end of year	104	0
Interest cost	20	0
Participant contributions	21	0
Benefits paid	(11)	0
Actuarial gain	18	0
Exchange rate changes	163	0
Benefit obligation at end of year	2,053	1,738	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	895	0
Acquisitions	0	895
Actual return on plan assets	57	0
Employer (reimbursement)/contributions	57	0
Participant contributions	21	0
Benefits paid	(11)	0
Exchange rate changes	84	0
Fair value of plan assets at end of year	$ 1,103	$ 895	$ 0