REVENUE - Contract Balances (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Trade accounts receivable, net	[1]	$ 194,214	$ 194,066
Contract assets		4,859	5,242	[2]
Contract liabilities	[3]	961	$ 930
Contract asset, increase from beginning of period		$ 400

[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.