Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
Federal tax credits	(18.20%)	(19.00%)	(11.40%)
State and local taxes, net of federal tax benefit	4.80%	4.20%	3.90%
Flow through depreciation and cost basis differences	0.20%	0.00%	(2.30%)
Other	(1.20%)	0.50%	0.80%
Effective tax rate	20.60%	20.70%	26.00%