Income Taxes - General (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the entity's provision for income taxes at statutory rates to the provision for income taxes at the entity's effective tax rate
Federal income tax statutory rate (as a percent)	21.00%	35.00%	35.00%
Less: Rate attributable to non-controlling interest members (as a percent)	(12.30%)	(22.00%)	(24.80%)
State income taxes, net of federal benefit (as a percent)	2.30%	2.20%	1.60%
Tax rate revaluation	(2.20%)	(8.00%)	0.00%
Other (as a percent)	(0.10%)	0.10%	0.20%
Effective tax rate (as a percent)	8.70%	7.30%	12.00%