CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues [Abstract]
Product sales, net	$ 23,537	$ 21,779
Costs and expenses:
Cost of product sales	267	131
Research and development	28,911	26,255
Selling, general and administrative	18,036	14,632
Total costs and expenses	47,214	41,018
Loss from operations	(23,677)	(19,239)
Interest expense	(5,903)	(5,600)
Other income	549	494
Net loss	(29,031)	(24,345)
Comprehensive loss	$ (29,031)	$ (24,345)
Basic and diluted net loss per share (USD per share)	$ (0.53)	$ (0.50)
Weighted-average shares used to compute basic and diluted net loss per share ( in shares)	54,299,813	49,014,009
Revenue, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Cost, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember