LONG-TERM DEBT, DERIVATIVES AND LETTERS OF CREDIT - Components of Convertible Debt Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Amortization of debt discount and issuance costs			$ 1,434	$ 381
Total interest expense	$ 6,369	$ 3,211	13,899	$ 9,554
Convertible debt
Debt Instrument [Line Items]
Coupon interest	1,949		1,949
Amortization of debt discount and issuance costs	919		919
Total interest expense	$ 2,868		$ 2,868
Effective interest rate	9.12%		9.12%