Income Taxes - Income Tax Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory U.S. federal tax rate	21.00%	35.00%	35.00%
State taxes, net of federal benefit	4.70%	3.30%	5.40%
Impact of 2017 tax reform on deferred tax balance	0.00%	4.60%	0.00%
Equity-based compensation expense	(1.50%)	(0.80%)	16.20%
Contingent consideration	7.20%	4.40%	41.50%
Other permanent items, net	(1.40%)	(0.50%)	11.90%
Tax credits	6.20%	0.70%	(19.20%)
Write-down of acquired state net operating losses	0.00%	0.00%	67.70%
Valuation allowance	(67.40%)	(0.80%)	(68.30%)
Other, net	0.60%	0.20%	(3.90%)
Effective tax rate	(30.60%)	46.10%	86.30%