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Employee benefit plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Defined contribution plan, vest percentage	100.00%
Company contributions to 401 (k) plan	$ 0.2	$ 0.2	$ 0.1

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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.

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No definition available.

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- Definition

Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

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No definition available.

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