Income taxes - Reconciliation (Details) - EUR (€) € in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of profit before income taxes to income tax
Loss before income tax	€ (15,569)	€ (13,939)	€ (8,683)
Prevailing statutory tax rate (as a percent)	28.00%
Tax expense at prevailing statutory rate (28%)	€ 4,359	3,903	2,431
Non-deductible expenses	(732)	(447)	(196)
Non-taxable income	80		242
Tax-rate related differences	(69)	(198)	(128)
Unrecognized temporary differences and tax losses	(3,550)	(3,297)	(2,413)
Income tax (expense) income	€ 88	€ (39)	€ (64)

The applicable income tax rate.

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The aggregate amount included in the determination of profit (loss) for the period in respect of current tax and deferred tax. [Refer: Current tax expense (income); Deferred tax expense (income)]

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The profit (loss) before tax expense or income. [Refer: Profit (loss)]

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No definition available.

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to changes in the tax rate. [Refer: Accounting profit]

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to expenses not deductible in determining taxable profit (tax loss). [Refer: Accounting profit]

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to revenues that are exempt from taxation. [Refer: Accounting profit]

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to tax losses. [Refer: Accounting profit]

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The product of the accounting profit multiplied by the applicable tax rate(s). [Refer: Accounting profit; Applicable tax rate]

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