Summary of Significant Accounting Policies - Anti-dilutive securities (Details) - shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities	3,997,316	3,162,767	2,495,268
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities	3,988,716	3,152,267	2,386,538
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities	8,600	10,500	108,730

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

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