Income Taxes Reconciliation of statutory federal income tax rate to effective income tax rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes at federal statutory rate	35.00%	35.00%	35.00%
Effect of state and local income taxes, net of federal tax	3.10%	3.30%	2.80%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	18.30%	0.50%	0.30%
Deferred tax asset valuation allowance	(1.10%)	(2.20%)	0.40%
Tax contingencies	(1.00%)	(1.30%)	0.10%
Other	(1.90%)	0.20%	0.90%
Effective rate	52.40%	35.50%	39.50%