Income Taxes (Details)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Income Taxes
Effective tax rate on income before provision for income taxes including income attributable to noncontrolling interests (as a percent)	35.10%	42.10%
Effective tax rate on income before provision for income taxes and noncontrolling interests (as a percent)	36.50%	43.00%
U.S. federal statutory income tax rate (as a percent)	35.00%
Minimum period of statute of limitations of state and foreign jurisdictions	3 years
Maximum period of statute of limitations of state and foreign jurisdictions	5 years