Income Taxes - Reconciliation between Statutory Income Tax Rate and Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. Statutory Tax Rate	21.00%	35.00%	35.00%
Increase Due to State and Local Taxes	3.60%	3.10%	4.80%
Rate Benefits As Limited Liability Company Flow Through	(2.60%)	(2.30%)	(5.90%)
Foreign Taxes	0.20%	(1.10%)	0.70%
Non-Deductible Expenses	1.20%	1.60%	9.90%
ASU 2016-09 Benefit for Stock Compensation	(4.20%)	(5.50%)	(0.00%)
Tax Cuts and Jobs Act - Reduction to Tax Receivable Agreement Liability	(0.00%)	(5.60%)	(0.00%)
Tax Cuts and Jobs Act - Primarily Related to the Re-measurement of Net Deferred Tax Assets	0.10%	32.70%	0.00%
Valuation Allowances	0.30%	1.10%	0.00%
Other Adjustments	0.10%	0.10%	0.00%
Effective Income Tax Rate	19.70%	59.10%	44.50%