Net loss per share - Narrative (Details) - $ / shares	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Convertible Notes \| Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price (in dollars per share)	$ 0.0464
Convertible Notes \| Convertible Senior Notes Due 2026
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Initial conversion price (in dollars per share)	$ 0.03084
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)	989,000	590,000
RSU Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)	375,000	0
Convertible Debt Securities \| Convertible Notes \| Convertible Senior Notes due 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)	638,051
Convertible Debt Securities \| Convertible Notes \| Convertible Senior Notes Due 2026
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding (in shares)	3,700,272

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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