Fair value of financial instruments - Fixed Rate Debt (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
2027 Senior Unsecured Notes
Debt Instrument [Line Items]
Carrying value	$ 600.0	$ 600.0
2027 Senior Unsecured Notes \| Level 3
Debt Instrument [Line Items]
Fair value	579.1	579.0
2029 Senior Unsecured Notes
Debt Instrument [Line Items]
Carrying value	400.0	400.0
2029 Senior Unsecured Notes \| Level 3
Debt Instrument [Line Items]
Fair value	406.3	412.2
2032 Senior Unsecured Notes
Debt Instrument [Line Items]
Carrying value	400.0	400.0
2032 Senior Unsecured Notes \| Level 3
Debt Instrument [Line Items]
Fair value	$ 406.3	$ 416.0

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details