STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
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 Gains (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
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
Share-Based Compensation		12,774			12,774
Foreign Currency Translation Adjustments			15		15
Unrealized Gains (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
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	534			$ 535
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	158,152
Shares Issued in Connection with Cantor Agreement	$ 3	13,943			13,946
Shares Issued in Connection with Cantor Agreement (in shares)	3,303,800
Shares Issued in Connection with the Kolltan Acquisition	$ 18	73,379			73,397
Shares Issued in Connection with the Kolltan Acquisition (in shares)	18,257,996
Shares Issued in Connection with Kolltan Severance		427			427
Shares Issued in Connection with Kolltan Severance (in shares)	111,111
Share-Based Compensation		15,317			15,317
Unrealized Gains (Losses) on Marketable Securities			234		234
Net Loss				(128,530)	(128,530)
Balance at Dec. 31, 2016	$ 121	$ 982,255	$ 2,541	$ (719,486)	$ 265,431
Balance (in shares) at Dec. 31, 2016	120,516,654				120,516,654