Income taxes (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) jurisdiction	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Income taxes.
Provision for (benefit from) income taxes	$ 1,457,000	$ (1,524,000)	$ (1,663,000)
Increase (decrease) in income taxes	2,400,000
Increases recorded to income tax provision	26,500,000
U.K. operating loss carryforwards	266,200,000
Uncertain tax positions	0	0
Interest and penalties accrued	$ 0	$ 0
State
Income taxes.
Number of jurisdictions | jurisdiction	11