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Share-based compensation - Additional Information (Details) - USD ($) | 6 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019 | Jun. 11, 2020 | Jun. 07, 2018 | Sep. 17, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Share based compensation expense | $ 300,000 | $ 600,000 |  |  |  |
Common stock reserved for issuance | 3,077,400 |  |  |  |  |
Options granted | 0 | 284,800 | 3,164,800 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $ 800,000 |  | $ 700,000 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | 100,000 |  | $ 300,000 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $ 0 | $ 11,100,000 |  |  |  |
Stock option vesting period | 2 years |  |  |  |  |
Minimum |  |  |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Contractual term | 3 years |  |  |  |  |
Maximum |  |  |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Contractual term | 10 years |  |  |  |  |
2014 Stock Incentive Plan |  |  |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  |  | 3,000,000
Share-based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock |  |  |  |  |  | $ 110
2018 Stock Incentive Plan |  |  |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Common stock reserved for issuance |  |  |  |  | 4,000,000 |
Share-based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock |  |  |  |  | $ 110 |
2020 Stock Incentive Plan |  |  |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |  |  |
Common stock reserved for issuance |  |  |  | 3,000,000 |  |
Share-based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock |  |  |  | $ 110 |  |

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- Definition Intrinsic value of equity-based compensation awards not vested. Stock units + References No definition available. + Details
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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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