Income tax Effective Income Tax Rate Reconcilitation (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%
Federal tax credits	(10.50%)	(8.90%)
State and local taxes, net of federal tax benefit	8.90%	8.80%
Flow through depreciation and cost basis differences	0.70%	0.30%
Excess deferred tax amortization	(4.50%)	(3.20%)
Other	0.00%	(8.20%)
Effective tax rate	15.50%	8.60%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	(0.10%)	(1.20%)