Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information
Net product sales	$ 15,393	$ 12,503	$ 11,363	$ 10,729	$ 9,222	$ 7,100	$ 5,179	$ 5,631	$ 49,988	$ 27,132	$ 10,033
Net product sales	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Gross profit (loss)	$ 7,631	$ 5,546	$ 4,376	$ 5,508	$ 5,582	$ 4,277	$ 2,362	$ 881	$ 23,060	$ 13,102	$ (1,701)
Net loss attributable to common stock	$ (9,337)	$ (12,695)	$ (15,207)	$ (14,436)	$ (13,652)	$ (16,254)	$ (18,645)	$ (17,221)
Weighted average common shares outstanding used to compute net loss per share, basic and diluted	41,415,358	29,625,792	29,008,909	28,996,956	28,746,608	27,884,983	22,613,382	19,624,712	32,288,555	24,751,091	16,052,390
Net loss per share of common stock, basic and fully diluted	$ (0.23)	$ (0.43)	$ (0.52)	$ (0.50)	$ (0.47)	$ (0.58)	$ (0.82)	$ (0.88)	$ (1.60)	$ (2.66)	$ (5.16)