Equity - Narrative (Details)				3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 18, 2019 $ / shares shares	Aug. 10, 2017 USD ($)	Jun. 27, 2017 $ / shares shares	Jun. 30, 2020 USD ($) vote $ / shares shares	Mar. 31, 2019 shares	Jun. 30, 2020 USD ($) vote $ / shares shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / shares shares
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)						100,847,810
Shares issued, value | $						$ 0	$ 30,942,000
Class of warrant or right, outstanding (in shares)				14,841,100,000		14,841,100,000		31,426,248,000
Warrant liabilities | $				$ 32,767,000		$ 32,767,000		$ 41,549,000
Exercise price (in dollars per share) | $ / shares				$ 1.56		$ 1.56		$ 1.12
Issuance of common stock upon exercise of common warrants (in shares)						16,585,148,000
Common stock, shares authorized (in shares)				200,000,000		200,000,000		200,000,000
Common stock, par value (in dollars per share) | $ / shares				$ 0.0001		$ 0.0001		$ 0.0001
Number of votes per share that common stockholders are entitled to | vote				1		1
Dividends declared or paid on common stock | $						$ 0
December 2019 Financing
Subsidiary, Sale of Stock [Line Items]
Sale common stock | $						$ 65,600,000
Sale of stock, number of shares issued in transaction (in shares)	37,634,883
Share price (in dollars per share) | $ / shares	$ 1.46			$ 0.125		$ 0.125
Class of warrant or right, outstanding (in shares)				22,988,501		22,988,501
Warrant Issued | $						$ 40,700,000
Warrant liabilities | $				$ 41,500,000		41,500,000
Warrant, increase (decrease) in equity, amount | $				$ (8,400,000)
Issuance costs | $						$ 4,400,000
Exercise price (in dollars per share) | $ / shares				$ 1.46		$ 1.46
At-The-Market Offering
Subsidiary, Sale of Stock [Line Items]
Public securities offering, amount authorized | $		$ 200,000,000.0
Sale common stock | $						$ 50,000,000
Sale of stock, number of shares issued in transaction (in shares)						1,069,486		615,453
Share price (in dollars per share) | $ / shares				$ 2.16		$ 2.16		$ 1.84
Shares issued, value | $						$ 2,137,000	$ 372,000	$ 1,000,000.0
2017 PIPE
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)			2,750,000
Share price (in dollars per share) | $ / shares			$ 16.00
Shares issued, value | $						$ 47,100,000
Common stock, shares authorized (in shares)				200,000,000		200,000,000
Common stock, par value (in dollars per share) | $ / shares				$ 0.0001		$ 0.0001
Springer Purchase Agreement
Subsidiary, Sale of Stock [Line Items]
Share price (in dollars per share) | $ / shares			$ 17.71
Springer Purchase Agreement | Common stock
Subsidiary, Sale of Stock [Line Items]
Stock issued (in shares)			338,791
Warrant
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)			79,130
Exercise price (in dollars per share) | $ / shares			$ 17.71
Warrants and rights outstanding, term			5 years
Share price (in dollars per share) | $ / shares			$ 0.125
Common stock
Subsidiary, Sale of Stock [Line Items]
Stock issued (in shares)					22,188,706
Issuance of common stock upon exercise of common warrants (in shares)				4,967,563		4,934,723
Pre-Funded Warrant [Member] | December 2019 Financing
Subsidiary, Sale of Stock [Line Items]
Class of warrant or right, number of warrants exercised (in shares)						8,342,128
Warrant
Subsidiary, Sale of Stock [Line Items]
Class of warrant or right, outstanding (in shares)				95,619,000		95,619,000		8,437,747,000
Class of warrant or right, number of warrants exercised (in shares)						8,210,180
Issuance of common stock upon exercise of common warrants (in shares)						8,342,128,000
Common Warrant [Member] | December 2019 Financing
Subsidiary, Sale of Stock [Line Items]
Class of warrant or right, number of warrants exercised (in shares)						32,840