Income tax Effective Income Tax Rate Reconcilitation (Details)	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%
Federal tax credits	(9.50%)	(16.20%)
State and local taxes, net of federal tax benefit	8.60%	9.10%
Flow through depreciation and cost basis differences	(0.50%)	0.20%
Excess deferred tax amortization	(2.00%)	(3.30%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	(0.40%)	(0.60%)
Effective tax rate	18.00%	10.70%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	0.80%	0.50%