Income Taxes - Income Tax Reconciliation (Details)	3 Months Ended	12 Months Ended
Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory U.S. federal tax rate		35.00%	35.00%	35.00%
State taxes, net of federal benefit		3.40%	6.40%	0.10%
Impact of 2017 tax reform on deferred tax balance		4.80%	0.00%	0.00%
Equity-based compensation expense		(1.00%)	34.00%	0.40%
Contingent consideration		4.50%	69.90%	4.70%
Transaction costs		0.00%	0.00%	3.90%
Other permanent items, net		(0.60%)	21.20%	3.20%
Tax credits		0.70%	(32.30%)	(1.70%)
Write-down of acquired state net operating losses		0.00%	114.20%	0.00%
Valuation allowance		(0.80%)	(115.20%)	(28.00%)
Other, net		0.20%	(5.80%)	0.10%
Effective tax rate	46.20%	46.20%	127.40%	17.70%

Effective Income Tax Rate Reconciliation, Nondeductible Expense, Contingent Consideration, Percent

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Effective Income Tax Rate Reconciliation, Nondeductible Expense, Transaction Costs, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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