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Equity - Narrative (Details) |  |  |  | 3 Months Ended | 6 Months Ended | 12 Months Ended
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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 |  |

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