INCOME TAXES - Income tax expense and net tax assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax expense [Line Items]
Total income tax expense (benefit)	$ 42,000	$ (29,486)	$ (7,542)	$ 6,340
Net current tax receivables (payables)		9,683		3,540
Taxes payable	(639)		(639)
Net deferred tax assets	4,438	39,775	4,438	103,313
Net tax assets	$ 3,799	49,458	3,799	106,853
U.S.
Income tax expense [Line Items]
Current income tax expense (benefit)		(5,401)	(6,207)	606
Deferred income tax expense (benefit)		15,288	18,495	(1,829)
Europe
Income tax expense [Line Items]
Current income tax expense (benefit)		10,409	10,249	7,451
Deferred income tax expense (benefit)		(49,833)	(30,079)	112
Other
Income tax expense [Line Items]
Current income tax expense (benefit)		$ 51	$ 0	$ 0