CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss)	Total
Balance beginning at Dec. 31, 2016	$ 136	$ 938,578	$ (929,996)	$ (2,450)	$ (11,814)	$ (5,546)
Balance beginning (in shares) at Dec. 31, 2016	13,585,070
Non-cash compensation cost for stock options, ESPP and restricted stock		19,809				19,809
Exercise of stock options/Purchases under ESPP	$ 1	1,151				1,152
Exercise of stock options/Purchases under ESPP, (in shares)	54,676
Issuance of common stock, net of issuance costs	$ 25	63,400				63,425
Issuance of common stock, net of issuance costs, (in shares)	2,544,495
Unrealized gain on marketable securities					(50)	(50)
Foreign currency translation adjustment					3,247	3,247
Net loss			(183,769)			(183,769)
Balance ending at Dec. 31, 2017	$ 162	1,023,532	(1,114,359)	(2,450)	(8,617)	(101,732)
Balance ending (in shares) at Dec. 31, 2017	16,184,241
Cumulative effect of adoption of ASU 2016-09		594	(594)
Non-cash compensation cost for stock options, ESPP and restricted stock		18,314				18,314
Exercise of stock options/Purchases under ESPP	$ 1	2,744				2,745
Exercise of stock options/Purchases under ESPP, (in shares)	120,561
Restricted stock cancelled (in shares)	(938)
Issuance of common stock, net of issuance costs	$ 29	100,031				100,060
Issuance of common stock, net of issuance costs, (in shares)	2,941,438
Unrealized gain on marketable securities					12	12
Foreign currency translation adjustment					(2,586)	(2,586)
Net loss			(184,748)			(184,748)
Balance ending at Dec. 31, 2018	$ 192	1,144,621	(1,299,107)	(2,450)	(11,191)	(167,935)
Balance ending (in shares) at Dec. 31, 2018	19,245,302
Non-cash compensation cost for stock options, ESPP and restricted stock		17,048				17,048
Exercise of stock options/Purchases under ESPP	$ 2	1,122		(132)		$ 992
Exercise of stock options/Purchases under ESPP, (in shares)	173,873
Restricted stock cancelled (in shares)						(76,661)
Fractional shares purchased in stock split				(1)		$ (1)
Issuance of common stock, net of issuance costs	$ 130	97,760				97,890
Issuance of common stock, net of issuance costs, (in shares)	12,980,177
Unrealized gain on marketable securities					5	5
Foreign currency translation adjustment					(1,322)	(1,322)
Net loss			(132,694)			(132,694)
Balance ending at Dec. 31, 2019	$ 324	$ 1,260,551	$ (1,431,801)	$ (2,583)	$ (12,508)	$ (186,017)
Balance ending (in shares) at Dec. 31, 2019	32,399,352