DEBT - Components of Interest Expense (Details) - 2016 Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
2016 Notes:
Amortization of the discount on the liability component	$ 2,104	$ 1,885	$ 4,168	$ 3,744
Cash interest related to the contractual interest coupon	892	824	1,780	1,669
Total	2,996	2,709	5,948	5,413
Amortization of debt discount (premium), interest costs capitalized	$ 100	200	200	400
Interest expense, debt, excluding amortization, interest costs capitalized		$ 100	$ 100	$ 200