REVENUE - Contract Balances (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Contract with Customer, Contract Asset, Contract Liability, and Receivable [Abstract]
Trade accounts receivable, net		$ 194,066	$ 245,617	[1]
Contract assets	[2]	5,242	4,671
Contract liabilities	[3]	930	1,224
Change in Contract with Customer, Asset [Abstract]
Contract asset, decrease from beginning of period		$ 500
Change in Contract with Customer, Liability [Abstract]
Contract liability, decrease from beginning of period			$ (900)

[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 consolidated balance sheet.

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