Income taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024
Operating loss carry-forward
Effective tax rate (as a percent)	22.09%		15.36%
Decrease in valuation allowance		$ 222.2
Federal
Operating loss carry-forward
Operating loss carryforwards	$ 1,200.0		$ 1,200.0
Operating loss carryforwards subject to expiration	789.8		789.8
Operating loss carryforwards not subject to expiration	421.7		421.7
State \| Oklahoma
Operating loss carry-forward
Operating loss carryforwards	538.0		538.0
Operating loss carryforwards subject to expiration	$ 34.6		$ 34.6

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are not subject to expiration dates.

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