Segment Reporting - Revenues and Operating Income by Reportable Segment (Details) $ in Millions	3 Months Ended								4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment											3
Segment Reporting Information [Line Items]
Revenues	$ 517.2	$ 452.0	$ 445.4	$ 416.8	$ 491.2	$ 432.4	$ 436.6	$ 411.3	$ 592.6	$ 748.6	$ 1,831.4	$ 1,771.5
Adjusted EBITDA									78.7	85.6	258.6	234.8
Net income attributable to non-controlling interests	$ (41.8)	$ (26.6)	$ (27.9)	$ (23.6)	$ (40.7)	$ (23.0)	$ (23.8)	$ (22.6)	(39.6)	(42.1)	(119.9)	(110.1)
Depreciation and amortization									(21.8)	(30.1)	(76.5)	(67.4)
Interest expense, net									(48.7)	(69.0)	(178.9)	(147.0)
Equity-based compensation expense									(1.9)	(3.7)	(10.2)	(9.3)
Transaction, integration and acquisition costs									(9.2)	(7.7)	(36.1)	(34.0)
Gain (loss) on disposals and deconsolidation, net									0.0	(1.7)	4.4	(31.8)
(Loss) gain on litigation settlements and other litigation costs									8.7	3.8	(4.6)	(46.0)
Loss on debt extinguishment									0.0	(18.2)	(11.7)	0.0
Tax receivable agreement benefit (expense)									(25.3)	0.0	2.4	0.0
Impairment charges									0.0	0.0	(7.9)	(74.4)
Reserve adjustments									0.0	0.0	0.0	(2.7)
Contingent acquisition compensation expense									(2.0)	(5.1)	0.0	(1.5)
Gain on acquisition escrow release									(0.2)	(1.0)	0.0	0.0
Gain on amendment to tax receivable agreement									1.1	15.3	0.0	0.0
(Loss) income before income taxes									70.0	12.3	54.6	(69.2)
Transaction and integration costs									7.5	5.6	19.0	31.7
Acquisition costs									1.8	2.1	2.8	2.2
Start-up costs related to de novo surgical hospital											14.3
Other litigation costs											4.4
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA									(23.5)	(36.0)	(74.3)	(80.2)
Surgical facility services | Operating Segments
Segment Reporting Information [Line Items]
Revenues									564.4	688.7	1,748.2	1,682.4
Adjusted EBITDA									103.8	125.9	328.9	309.5
Ancillary services | Operating Segments
Segment Reporting Information [Line Items]
Revenues									24.7	52.3	79.4	79.6
Adjusted EBITDA									(2.3)	(6.5)	2.6	3.0
Optical services | Operating Segments
Segment Reporting Information [Line Items]
Revenues									3.5	7.6	3.8	9.5
Adjusted EBITDA									$ 0.7	$ 2.2	$ 1.4	$ 2.5