CONVERTIBLE NOTES (Schedule of Interest Expense Recognized) (Details) - 2013 Notes [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Contractual interest expense	$ 501	$ 2,943	$ 3,105
Amortization of debt issuance costs and debt discount	71	421	444
Total	$ 572	$ 3,364	$ 3,549