Income tax Effective Income Tax Rate Reconcilitation (Details)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%
Federal tax credits	(9.30%)	(10.50%)
State and local taxes, net of federal tax benefit	9.00%	8.90%
Flow through depreciation and cost basis differences	1.00%	0.70%
Excess deferred tax amortization	(3.70%)	(4.50%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	(2.10%)	(0.10%)
Effective tax rate	15.90%	15.50%