REVENUE RECOGNITION AND RECEIVABLES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2018
Contracts
Net deferred tax liabilities	$ 10,675	$ 8,680
Retained earnings	516,901	541,890
Minority interest	$ 108,687	$ 129,961
Change | ASU 2014-09
Contracts
Contract asset			$ 1,600
Contract liability			200
Contract acquisition costs			1,500
Net deferred tax liabilities			300
Retained earnings			1,500
Minority interest			1,100
Change | ASU 2014-09 | Prepayments and other current assets
Contracts
Contract asset			1,200
Contract acquisition costs			900
Change | ASU 2014-09 | Other non current assets
Contracts
Contract asset			400
Contract acquisition costs			$ 600