REVENUE - Contract Balances (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Trade accounts receivable, net		$ 217,461	$ 194,066	[1]
Contract assets	[2]	1,453	5,242
Contract liabilities	[3]	893	$ 930
Contract asset, decrease from beginning of period		$ 3,800

[1] Includes billed and unbilled amounts, net of allowance for credit losses. See Note 3 for details.

[2] Included in the “Prepaid expenses and other current assets” line on the condensed consolidated balance sheets.

[3] Included in the “Other accrued liabilities” line of the condensed consolidated balance sheets.