Revenue from contracts with customers - Revenue streams - Parenthetical (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Interchange fees	$ 22.2	$ 22.2	$ 45.5	$ 45.3	$ 43.3
Intersegment Transaction
Revenue From Contract With Customer Excluding Assessed Tax			$ 4.5	$ 5.0	$ 5.0

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details