LONG-TERM DEBT / INTEREST EXPENSE - Components of Convertible Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Aug. 10, 2015
Liability component
Total debt	$ 862,565	$ 1,152,322
Equity component
Debt instrument convertible carrying value	100
Notes (net of $3.9 million and $11.5 million conversion feature and $0.5 million and $1.6 million discount)
Liability component
Conversion feature	(3,900)	(11,500)
Notes (net of $3.9 million and $11.5 million conversion feature and $0.5 million and $1.6 million discount) | Notes (net of $3.9 million and $11.5 million conversion feature and $0.5 million and $1.6 million discount)
Liability component
Principal	159,097	188,565	$ 287,500
Conversion feature	(3,898)	(11,489)
Discount related to debt issuance costs	(524)	(1,572)
Total debt	154,675	175,504
Equity component
Conversion feature	49,680	49,680
Debt issuance costs	(1,421)	(1,421)
Deferred taxes	(16,540)	(16,620)
Net amount recorded in additional paid-in capital	$ 31,719	$ 31,639