Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Federal statutory tax rate	21.00%	35.00%	35.00%
Federal tax credits	(16.70%)	(14.00%)	(18.20%)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	0.00%	6.10%	0.00%
State and local taxes, net of federal tax benefit	6.50%	5.00%	4.80%
Flow through depreciation and cost basis differences	1.50%	1.50%	0.20%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization, Percent	(4.10%)	0.00%	0.00%
Other	(0.80%)	(2.10%)	(1.20%)
Effective tax rate	7.40%	31.50%	20.60%