LONG-TERM DEBT - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest expense, net
Amortization of deferred financing costs	$ (14,856)	$ (11,295)	$ (3,434)
Capitalized interest	3,163	27,602	35,170
Commitment fees	(629)	(5,201)	(2,713)
Interest rate swaps	3,607
Interest income	1,269	108	75
Interest expense, net	(82,764)	(49,627)	(15,982)
Refinancing Facility | Term Loan
Interest expense, net
Interest expense excluding amortization of deferred financing costs	(15,197)	(21,561)	(7,564)
Korean Export Credit Facility | Term Loan
Interest expense, net
Interest expense excluding amortization of deferred financing costs	(27,046)	(13,224)	(922)
Senior Notes | Term Loan
Interest expense, net
Interest expense excluding amortization of deferred financing costs	(20,845)	(18,612)	(16,529)
Sinosure Credit Facility | Term Loan
Interest expense, net
Interest expense excluding amortization of deferred financing costs	$ (12,230)	$ (7,444)	(19)
Fully repaid credit facilities
Interest expense, net
Interest expense excluding amortization of deferred financing costs			$ (20,046)