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Goodwill and other identifiable intangible assets - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets
Accumulated goodwill impairment losses	$ 8.0	$ 8.0
Identifiable intangible asset amortization expense	0.8	$ 0.7	$ 0.9
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity
2024	0.8
2025	0.8
2026	0.8
2027	0.8
2028	$ 0.8
Customer relationships
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity
Weighted average amortization period	15 years
Technology and trading related
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity
Weighted average amortization period	13 years