Income Taxes (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Federal income tax at statutory rate	21.00%	35.00%	21.00%	35.00%
State and local income taxes, less federal income tax benefit	5.00%	4.00%	4.70%	3.80%
Permanent differences	2.70%	0.80%	2.10%	1.10%
Valuation allowance	(0.10%)	0.10%	(0.10%)	0.20%
Uncertain tax positions	0.20%	0.20%	0.20%	0.20%
Non-controlling interest	(1.00%)	(1.60%)	(1.80%)	(1.80%)
Stock-based compensation	(2.70%)	(2.30%)	(2.60%)	(0.90%)
Other	(0.30%)	(0.10%)	0.90%	(0.20%)
Total effective income tax rate	24.80%	36.10%	24.40%	37.40%