REVENUE - Contract Balances (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Contract with Customer, Asset and Liability [Abstract]
Trade accounts receivable, net	[1]	$ 245,617	$ 268,352
Contract assets	[2]	4,671	5,745
Contract liabilities	[3]	1,224	$ 1,784
Change in Contract with Customer, Asset [Abstract]
Contract asset, decrease from beginning of period		1,100
Change in Contract with Customer, Liability [Abstract]
Contract liability, decrease from beginning of period		$ 600

[1] Includes billed and unbilled amounts, net of allowance for doubtful accounts. 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.