Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective income tax rate reconciliation [Abstract]
U.S. federal statutory income tax rate	35.00%	35.00%	35.00%
U.S. state and local income taxes, net of federal income tax benefit	2.20%	5.60%	2.20%
Income of pass-through entities allocated to non-controlling interests	(5.10%)	(4.80%)	(5.40%)
Section 199 - Domestic Production Activities deduction	(2.50%)	(2.40%)	(2.50%)
2017 Tax Act	6.10%
Foreign tax law changes	2.30%
Foreign earnings at other than U.S. rates	(2.00%)	(0.30%)	0.20%
Other	1.90%	0.60%	1.10%
Effective income tax rate	37.90%	33.70%	30.60%