REVENUE - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract asset (current)	$ 15,914	$ 16,245
Increase / (decrease) in contract asset (current)	(331)
Contract asset (long-term)	0	0
Increase / (decrease) in contract assets (long-term)	0
Contract liability (current)	66,782	79,305
Increase / (decrease) in contract liability (current)	(12,523)
Contract liability (long-term)	22,035	9,779
Increase / (decrease) in contract liability (long-term)	12,256
Revenue recognized previously included in current contract liabilities	59,600
Revenue recognized previously included in current contract liabilities at beginning of the year	39,100
Unearned revenue associated with outstanding contracts	487	515
Estimated revenue to be recognized in 2020	55
Estimated revenue to be recognized in 2021	131
Estimated revenue to be recognized after 2021	301
Allowance for Credit Loss [Abstract]
Accounts and note receivable	593,418	558,428
Accounts and notes receivable, allowance for doubtful accounts (in dollars)	$ 7,440	$ 3,626