Property and equipment, net - Summary (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 1,473		$ 1,253
Less: Accumulated depreciation	(937)		(780)
Property and equipment, net	536		473
Depreciation	156	$ 131
Computer equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	201		201
Office and other equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	329		260
Laboratory equipment
Property, Plant and Equipment [Line Items]
Gross property and equipment	880		729
Leasehold improvements
Property, Plant and Equipment [Line Items]
Gross property and equipment	$ 63		$ 63

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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