Equity - Issuance of stock and warrants (Details) $ / shares in Units, $ in Thousands									1 Months Ended	12 Months Ended
	Sep. 23, 2019 USD ($) $ / shares shares	Jun. 18, 2019 USD ($) $ / shares shares	Nov. 28, 2018 USD ($) item $ / shares shares	Aug. 03, 2018 USD ($) $ / shares shares	Jul. 12, 2018 USD ($) $ / shares shares	Jun. 21, 2018 USD ($) $ / shares shares	Jun. 09, 2018 USD ($) $ / shares shares	Apr. 03, 2018 USD ($) $ / shares shares	Apr. 30, 2019 shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Mar. 29, 2019 $ / shares	Sep. 20, 2018 $ / shares shares	Jun. 20, 2018 shares
Equity
Proceeds from exercise of warrants | $										$ 142	$ 513
Warrants expired (in shares)										139	1
Private placements
Equity
Net proceeds from issuance of stock | $		$ 6,900
Registered direct offering
Equity
Number of healthcare focused institutional investors | item			2
Net proceeds from issuance of stock | $			$ 9,100	$ 500	$ 2,200	$ 1,300	$ 1,200	$ 5,100
Redemption of convertible preferred stock | $						$ 500
Series A warrants
Equity
Warrant exercise price (in dollars per share) | $ / shares												$ 1.20
Series A warrants | Private placements
Equity
Warrant exercise price (in dollars per share) | $ / shares		$ 2.64
Series A warrants | Registered direct offering
Equity
Number of shares in exchange of warrant exercise			66,667
Warrant exercise price (in dollars per share) | $ / shares			$ 180.00
Series B warrants | Private placements
Equity
Warrant exercise price (in dollars per share) | $ / shares		2.40
Prefunded warrants | Registered direct offering
Equity
Purchase price (in dollars per share) | $ / shares			148.80
Warrant exercise price (in dollars per share) | $ / shares			$ 1.20
Series C pre-funded warrants | Private placements
Equity
Warrant exercise price (in dollars per share) | $ / shares		$ 0.12
Placement agent warrants | Registered direct offering
Equity
Number of shares in exchange of warrant exercise			4,667
Warrant exercise price (in dollars per share) | $ / shares			$ 187.50
Unregistered Shares | Series E warrants | Private placements
Equity
Number of shares in exchange of warrant exercise	3,333,334
Series D convertible preferred stock
Equity
Redemption of stock (in shares)						500
Preferred stock outstanding														5,250
Common Stock | Private placements
Equity
Number of shares in exchange of warrant exercise	69,167
Stock issued (in shares)		130,000
Purchase price (in dollars per share) | $ / shares		$ 2.40
Common Stock | Registered direct offering
Equity
Stock issued (in shares)			5,584	60	74	28	23
Purchase price (in dollars per share) | $ / shares			$ 150.00	$ 10,080.00	$ 34,440.00	$ 51,576.00	$ 65,856.00
Common Stock | Series A warrants | Private placements
Equity
Number of shares in exchange of warrant exercise		3,333,334
Common Stock | Series B warrants | Private placements
Equity
Number of shares in exchange of warrant exercise		3,333,334
Common Stock | Series C pre-funded warrants | Private placements
Equity
Number of shares in exchange of warrant exercise		3,203,334
Common Stock | Investor Warrants | Registered direct offering
Equity
Purchase price (in dollars per share) | $ / shares					$ 2,100.00	$ 2,100.00	$ 2,100.00
Common Stock | Placement agent warrants | Private placements
Equity
Number of shares in exchange of warrant exercise		233,334
Warrant exercise price (in dollars per share) | $ / shares		$ 3.00
Warrants
Equity
Number of shares in exchange of warrant exercise													119
Warrant exercise price (in dollars per share) | $ / shares													$ 756.00
Warrants | Private placements
Equity
Proceeds from exercise of warrants | $	$ 6,900
Warrants | Series B warrants | Private placements
Equity
Number of warrants to be exercised early	3,333,334
Warrants | Prefunded warrants | Registered direct offering
Equity
Number of shares in exchange of warrant exercise			61,084
Warrants | Series C pre-funded warrants | Private placements
Equity
Purchase price (in dollars per share) | $ / shares		$ 2.28
Warrants | Series F prefunded warrants | Private placements
Equity
Number of shares in exchange of warrant exercise	3,264,167
Warrants | Series E warrants
Equity
Term of warrants	5 years
Warrants | Series E warrants | Private placements
Equity
Warrant exercise price (in dollars per share) | $ / shares	$ 6.00
Warrants | Investor Warrants
Equity
Warrants expired (in shares)									137
Warrants | Investor Warrants | Registered direct offering
Equity
Number of shares in exchange of warrant exercise				60	74	28	17	139
Warrant exercise price (in dollars per share) | $ / shares				$ 18,480.00	$ 34,608.00	$ 51,744.00	$ 66,024.00	$ 189,000.00
Warrants | Placement agent warrants
Equity
Warrant exercise price (in dollars per share) | $ / shares	$ 6.00
Number of warrants issued	233,334
Warrants | Placement agent warrants | Registered direct offering
Equity
Number of shares in exchange of warrant exercise				5	6	2	2
Warrant exercise price (in dollars per share) | $ / shares				$ 12,600.00	$ 45,679.20	$ 67,032.00	$ 84,168.00
Preferred Stock | Series D convertible preferred stock
Equity
Redemption of stock (in shares)											(500)
Preferred Stock | Series D convertible preferred stock | Registered direct offering
Equity
Stock issued (in shares)								6,000
Purchase price (in dollars per share) | $ / shares								$ 1,000