STOCKHOLDERS' EQUITY (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 31, 2016
Stockholders' Equity
Maximum aggregate offering price of securities in shelf registration statement	$ 250,000
Common Stock, Shares Issued	120,516,654	98,685,595
Shares Issued in Connection with Supply Agreement			$ 2,000
Research and development expense	$ 102,726	$ 100,171	$ 104,381
Net proceeds from sale of stock		188,840
Other assets	2,134	1,428
Prepaid and other current assets	4,009	4,077
Net proceeds from sale of common stock	$ 13,946	$ 188,840
Preferred stock, shares authorized	3,000,000	3,000,000
Amended and restated supply agreement
Stockholders' Equity
Common Stock, Shares Issued			152,172
Shares Issued in Connection with Supply Agreement			$ 2,000
Research and development expense	$ 1,600	$ 300	$ 100
Research and collaboration agreement
Stockholders' Equity
Payment for research and collaboration agreement and investment in company	3,500
Other assets	1,800
Prepaid and other current assets	1,700
Prepaid research	$ 700
Cantor agreement
Stockholders' Equity
Common stock issued (in shares)	3,303,800
Net proceeds from sale of common stock	$ 13,900
Cantor agreement | Maximum
Stockholders' Equity
Common stock available for sale (in shares)				60,000,000
Underwritten Public Offering
Stockholders' Equity
Common stock issued (in shares)		8,337,500
Net proceeds from sale of stock		$ 188,800
Class C Preferred Stock
Stockholders' Equity
Preferred stock, shares authorized	3,000,000
Series C-1 Preferred Stock
Stockholders' Equity
Preferred stock, shares authorized	350,000