STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2012	$ 64	$ 357,094	$ 2,745	$ (264,129)	$ 95,774
Balance (in shares) at Dec. 31, 2012	64,359,513
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	5,402			5,403
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	840,228
Shares Issued in Connection with Cantor Agreement	$ 2	17,132			17,134
Shares Issued in Connection with Cantor Agreement (in shares)	2,433,608
Shares Issued in Underwritten Offering	$ 22	278,541			$ 278,563
Shares Issued in Underwritten Offering (in shares)	21,613,483				21,613,483
Share-Based Compensation		4,548			$ 4,548
Foreign Currency Translation Adjustments			(3)		(3)
Unrealized Losses on Marketable Securities			(74)		(74)
Net Loss				(81,550)	(81,550)
Balance at Dec. 31, 2013	$ 89	662,717	2,668	(345,679)	319,795
Balance (in shares) at Dec. 31, 2013	89,246,832
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	1,170			1,171
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	193,775
Shares Issued in Connection with Supply Agreement		2,000			2,000
Shares Issued in Connection with Supply Agreement (in shares)	152,172
Share-Based Compensation		6,852			6,852
Foreign Currency Translation Adjustments			(5)		(5)
Unrealized Losses on Marketable Securities			(73)		(73)
Net Loss				(118,080)	(118,080)
Balance at Dec. 31, 2014	$ 90	672,739	2,590	(463,759)	$ 211,660
Balance (in shares) at Dec. 31, 2014	89,592,779				89,592,779
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	4,310			$ 4,311
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	755,316
Shares Issued in Underwritten Offering	$ 8	188,832			$ 188,840
Shares Issued in Underwritten Offering (in shares)	8,337,500				8,337,500
Share-Based Compensation		12,774			$ 12,774
Foreign Currency Translation Adjustments			15		15
Unrealized Losses on Marketable Securities			(298)		(298)
Net Loss				(127,197)	(127,197)
Balance at Dec. 31, 2015	$ 99	$ 878,655	$ 2,307	$ (590,956)	$ 290,105
Balance (in shares) at Dec. 31, 2015	98,685,595				98,685,595