Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
Federal tax credits	(11.80%)	(12.70%)	(10.40%)
State and local taxes, net of federal tax benefit	3.50%	2.60%	4.40%
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance	2.60%	0.00%	0.00%
Flow through depreciation and cost basis differences	2.40%	2.10%	0.10%
Other	(0.60%)	1.30%	1.20%
Effective tax rate	31.10%	28.30%	30.30%