RESTATEMENT OF PREVIOUSLY ISSUED FINANCIAL STATEMENTS - Narrative (Details) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($) entity	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase in cash and restricted cash				$ (40,159)	$ 24,443
Decrease in cumulative translation adjustment and other comprehensive income		$ (1,327)	$ (1,395)	$ (2,604)	$ (232)
Adjustments | Unvouchered Purchase Orders
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net reduction in accounts payable						$ 12,200
Adjustments | Reclassification
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in cumulative translation adjustment and other comprehensive income	$ 1,800
Increase in trade receivables	$ 1,800
2020 Acquisitions
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Number of businesses acquired | entity	4
Number of businesses acquired eligible for true-up consideration | entity	2
2020 Acquisitions | Adjustments | True-up Consideration
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrual for true-up consideration	$ 13,400
Increase in goodwill from acquisitions	13,400
2020 Acquisitions | Adjustments | Reclassification
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase in cash and restricted cash	2,000
Decrease in cumulative translation adjustment and other comprehensive income	$ 2,000