Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Product sales, net	$ 123	$ 326	$ 424	$ 684
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Costs and operating expenses:
Cost of product sales	$ 241	$ 397	$ 513	$ 860
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 8,225	$ 12,714	$ 13,875	$ 25,899
Selling, general and administrative	5,619	10,747	11,776	24,839
Total costs and operating expenses	14,085	23,858	26,164	51,598
Loss from operations	(13,962)	(23,532)	(25,740)	(50,914)
Interest income	409	311	763	615
Net loss	$ (13,553)	$ (23,221)	$ (24,977)	$ (50,299)
Net loss per share, basic and diluted	$ (0.44)	$ (0.77)	$ (0.82)	$ (1.66)
Weighted-average shares used to compute net loss per share, basic and diluted	30,594,288	30,269,190	30,581,481	30,263,042