Statements of Stockholders' (Deficit) - USD ($) $ in Thousands	Total	TEL AVIV STOCK EXCHANGE	Common Stock	Common Stock TEL AVIV STOCK EXCHANGE	Additional Paid-in Capital	Additional Paid-in Capital TEL AVIV STOCK EXCHANGE	Accumulated Other Comprehensive Income (Loss)	Deficit Accumulated During Development Stage
Beginning Balance at Dec. 31, 2014	$ (73,770)		$ 812		$ 2,420,216		$ (14)	$ (2,494,784)
Beginning Balance (in shares) at Dec. 31, 2014			81,212,000
Exercise of stock options	3,258		$ 3		3,255
Exercise of stock options (in shares)			340,000
Issuance of common shares from the release of restricted stock units	0		$ 1		(1)
Issuance of common shares from the release of restricted stock units (in shares)			144,000
Issuance of common shares pursuant to warrant exercises	10,123		$ 8		10,115
Issuance of common shares pursuant to warrant exercises (in shares)			843,000
Issuance of common shares under Employee Stock Purchase Plan	$ 887		$ 1		886
Issuance of common shares under Employee Stock Purchase Plan (in shares)	64,245		54,000
Stock-based compensation expense	$ 8,725				8,725
Restricted stock units taxes paid in cash	(1,856)				(1,856)
Capital contribution	40				40
Issuance of common shares pursuant to conversions of certain notes	7,926		$ 4		7,922
Issuance of common shares pursuant to conversions of certain notes (in shares)			375,000
Issuance of common stock for lender financing fees	160				160
Issuance of common stock for lender financing fees (in shares)			8,000
Discount on notes-for-stock exchange	169				169
Issuance of common stock	27,843	$ 34,710	$ 18	$ 28	27,825	$ 34,682
Issuance of common stock (Shares)			1,788,000	2,771,000
Return of loaned common stock			$ (18)		18
Return of loaned common stock (in shares)			(1,800,000)
Issuance of warrant liability	(202)				(202)
Reclassification of warrant liability to equity	109				109
Cumulative translation loss	(6)						(6)
Net (loss) income	(368,445)							(368,445)
Ending Balance at Dec. 31, 2015	(350,329)		$ 857		2,512,063		(20)	(2,863,229)
Ending Balance (in shares) at Dec. 31, 2015			85,735,000
Exercise of stock options	467		$ 1		466
Exercise of stock options (in shares)			55,000
Issuance of common shares from the release of restricted stock units	0		$ 1		(1)
Issuance of common shares from the release of restricted stock units (in shares)			131,000
Issuance of common shares under Employee Stock Purchase Plan	$ 426		$ 1		425
Issuance of common shares under Employee Stock Purchase Plan (in shares)	104,758		51,000
Stock-based compensation expense	$ 5,135				5,135
Restricted stock units taxes paid in cash	(165)				(165)
Issuance of direct placement - common stock and warrants (value)	50,000		$ 97		49,903
Issuance of direct placement - common stock and warrants (shares)			9,709,000
Issuance costs associated with direct placement	(2,037)				(2,037)
Issuance of warrant liability	(12,750)				(12,750)
Cumulative translation loss	(4)						(4)
Net (loss) income	125,664							125,664
Ending Balance at Dec. 31, 2016	(183,593)		$ 957		2,553,039		(24)	(2,737,565)
Ending Balance (in shares) at Dec. 31, 2016			95,681,000
Exercise of stock options	$ 24		$ 0		24
Exercise of stock options (in shares)	5,300		5,000
Issuance of common shares from the release of restricted stock units	$ 1		$ 2		(1)
Issuance of common shares from the release of restricted stock units (in shares)			135,000
Issuance of common shares under Employee Stock Purchase Plan	$ 236		$ 1		235
Issuance of common shares under Employee Stock Purchase Plan (in shares)	199,578		103,000
Stock-based compensation expense	$ 4,847				4,847
Restricted stock units taxes paid in cash	(127)				(127)
Issuance of common shares pursuant to conversions of certain notes	21,099		$ 115		20,984
Issuance of common shares pursuant to conversions of certain notes (in shares)			11,496,000
Issuance of direct placement — common stock	61,000		$ 102		60,898
Issuance of direct placement — common stock (shares)			10,167,000
Issuance costs associated with direct placement	(3,310)				(3,310)
Issuance of common stock	564		$ 2		562
Issuance of common stock (Shares)			173,000
Issuance costs associated with ATM placement	(17)				(17)
Reclassification of warrant liability to equity	1,893		$ 13		1,880
Reclassification of warrant liability to equity (in shares)			1,293,000
Amortization of shelf fees	(22)				(22)
Cumulative translation loss	6						6
Net (loss) income	(117,333)							(117,333)
Ending Balance at Dec. 31, 2017	$ (214,732)		$ 1,192		$ 2,638,992		$ (18)	$ (2,854,898)
Ending Balance (in shares) at Dec. 31, 2017			119,053,000