RESTRUCTURING - Summary of Restructuring Charges (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1,131,000	$ 469,000	$ 631,000	$ 368,000	$ 0	$ 2,599,000	$ 4,129,000
Asset impairments					0	1,100,000	1,600,000
Restructuring Plan 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0	2,599,000	4,204,000
Redundancy and employee severance and benefit arrangements
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0	1,575,000	2,228,000
Redundancy and employee severance and benefit arrangements | Restructuring Plan 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges					0	1,575,000	2,228,000
Asset impairments
Restructuring Cost and Reserve [Line Items]
Asset impairments					0	1,124,000	1,601,000
Asset impairments | Restructuring Plan 2018
Restructuring Cost and Reserve [Line Items]
Asset impairments					0	1,124,000	1,636,000
Consultants engaged in restructuring activities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, accrual adjustment					0	0	0
Lease loss reserves (benefit)
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, accrual adjustment					0	(100,000)	300,000
Lease loss reserves (benefit) | Restructuring Plan 2018
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, accrual adjustment					$ 0	$ (100,000)	$ 340,000