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Employee benefit plan - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2020 | Dec. 31, 2018 | Dec. 31, 2017
Retirement Benefits [Abstract] |  |  |  |
Defined contribution plan, vest percentage | 10000000.00% | 100.00% | 20000000.00% | 20000000.00%
Company contributions to 401 (k) plan |  | $ 0.3 |  |

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- References No definition available. + Details
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage of employer's matching contributions to a defined contribution plan that vests in a given year. + References No definition available. + Details
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