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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Net loss per share - Antidilutive securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Anti-dilutive securities
Anti-dilutive shares	2,999,284	17,015,958	16,843,783
Series A Preferred Stock
Anti-dilutive securities
Anti-dilutive shares		1,604,574	1,604,574
Series B Preferred Stock
Anti-dilutive securities
Anti-dilutive shares		5,730,612	5,730,612
Series C Preferred Stock
Anti-dilutive securities
Anti-dilutive shares		8,074,447	8,074,447
Options
Anti-dilutive securities
Anti-dilutive shares	2,999,284	1,606,325	1,434,150