CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance beginning at Dec. 31, 2014	$ 229,618	$ 2,393	$ 729,373	$ (493,093)	$ (2,450)	$ (6,605)
Balance beginning (in shares) at Dec. 31, 2014		239,287,294
Non-cash compensation cost for stock options, ESPP and restricted stock	13,431	$ 0	13,431	0	0	0
Exercise of stock options/Purchases under ESPP	4,801	$ 19	4,782	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,950,748
Restricted stock issued as compensation	0	$ 0	0	0	0	0
Restricted stock issued as compensation, shares		25,000
Issuance of common stock, net of issuance costs	204,275	$ 292	203,983	0	0	0
Issuance of common stock, net of issuance costs, shares		29,163,620
Unrealized gain (loss) on marketable securities	42	$ 0	0	0	0	42
Foreign currency translation adjustment	(2,561)	0	0	0	0	(2,561)
Net loss	(156,937)	0	0	(156,937)	0	0
Balance ending at Dec. 31, 2015	292,669	$ 2,704	951,569	(650,030)	(2,450)	(9,124)
Balance ending (in shares) at Dec. 31, 2015		270,426,662
Non-cash compensation cost for stock options, ESPP and restricted stock	19,160	$ 0	19,160	0	0	0
Exercise of stock options/Purchases under ESPP	3,802	$ 13	3,789	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,254,735
Restricted stock issued as compensation	0	$ 0	0	0	0	0
Restricted stock issued as compensation, shares		20,000
Payment of capped call transactions and costs	(38,521)	$ 0	(38,521)	0	0	0
Unrealized gain (loss) on marketable securities	54	0	0	0	0	54
Foreign currency translation adjustment	(2,744)	0	0	0	0	(2,744)
Net loss	(279,966)	0	0	(279,966)	0	0
Balance ending at Dec. 31, 2016	(5,546)	$ 2,717	935,997	(929,996)	(2,450)	(11,814)
Balance ending (in shares) at Dec. 31, 2016		271,701,397
Non-cash compensation cost for stock options, ESPP and restricted stock	19,809	$ 0	19,809	0	0	0
Exercise of stock options/Purchases under ESPP	1,152	$ 11	1,141	0	0	0
Exercise of stock options/Purchases under ESPP, shares		1,093,513
Issuance of common stock, net of issuance costs	63,425	$ 509	62,916	0	0	0
Issuance of common stock, net of issuance costs, shares		50,889,910
Unrealized gain (loss) on marketable securities	(50)	$ 0	0	0	0	(50)
Foreign currency translation adjustment	3,247	0	0	0	0	3,247
Net loss	(183,769)	0	0	(183,769)	0	0
Balance ending at Dec. 31, 2017	(101,732)	$ 3,237	1,020,457	(1,114,359)	(2,450)	(8,617)
Balance ending (in shares) at Dec. 31, 2017		323,684,820
Cumulative effect of adoption of ASU 2016-09	$ 0	$ 0	$ 594	$ (594)	$ 0	$ 0