Income taxes - Income Taxes Rate Reconciliation (Details)	1 Months Ended	12 Months Ended
Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of effect of applying the federal statutory rate to the net loss and the effective income tax rate
Statutory federal income tax rate	35.00%	21.00%	21.00%	34.00%
Earnings in jurisdictions taxed at rates different from the statutory U.S. federal tax rate		0.40%	1.00%	(12.00%)
Permanent differences		3.70%	0.40%	(0.10%)
Changes in valuation allowance		(25.10%)	(16.70%)	(21.50%)
Rate change due to TCJA				(0.40%)
Rate change due to Swedish tax reform			(5.70%)

No definition available.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deductions. Including, but not limited to, extraterritorial income exclusion deduction, qualified production activity deduction, dividend deduction, deduction for dividend paid to employee stock ownership plan, Medicare prescription drug benefit subsidy deduction, and other deductions.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to the temporary incentive for U.S. entities to repatriate accumulated foreign earnings under the American Jobs Creation Act of 2004.

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