Income taxes (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) jurisdiction	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Income taxes.
Benefit from income taxes	$ 1,524,000	$ 1,663,000	$ 724,000
Increases recorded to income tax provision	19,100,000
U.K. operating loss carryforwards	181,800,000
Uncertain tax positions	0	0
Interest and penalties accrued	$ 0	$ 0
State
Income taxes.
Number of jurisdictions | jurisdiction	11