Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Product sales, net	$ 192	$ 301
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Costs and operating expenses:
Cost of product sales	$ 213	$ 272
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 8,795	$ 5,650
Selling, general and administrative	3,278	6,157
Total costs and operating expenses	12,286	12,079
Loss from operations	(12,094)	(11,778)
Other income (expense)
Interest income	501	354
Interest expense	(391)	0
Net loss	$ (11,984)	$ (11,424)
Net loss per share, basic and diluted	$ (0.39)	$ (0.37)
Weighted-average shares used to compute net loss per share, basic and diluted	30,658,412	30,568,531