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, 2015	$ 292,669	$ 2,704	$ 951,569	$ (650,030)	$ (2,450)	$ (9,124)
Balance beginning (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 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 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
Non-cash compensation cost for stock options, ESPP and restricted stock	18,314	0	18,314	0	0	0
Exercise of stock options/Purchases under ESPP	2,745	$ 24	2,721	0	0	0
Exercise of stock options/Purchases under ESPP, shares		2,411,212
Restricted stock cancelled	0	$ 0	0	0	0	0
Restricted stock cancelled, shares		(18,750)
Issuance of common stock, net of issuance costs	100,060	$ 588	99,472	0	0	0
Issuance of common stock, net of issuance costs, shares		58,828,755
Unrealized gain on marketable securities	12	$ 0	0	0	0	12
Foreign currency translation adjustment	(2,586)	0	0	0	0	(2,586)
Net loss	(184,748)	0	0	(184,748)	0	0
Balance ending at Dec. 31, 2018	$ (167,935)	$ 3,849	$ 1,140,964	$ (1,299,107)	$ (2,450)	$ (11,191)
Balance ending (in shares) at Dec. 31, 2018		384,906,037