Segment Reporting - Revenues and Operating Income by Reportable Segment (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment			3
Segment Reporting Information [Line Items]
Revenues	$ 496,100,000	$ 452,000,000.0	$ 1,311,800,000	$ 1,314,200,000
Adjusted EBITDA	61,100,000	62,200,000	165,800,000	174,200,000
Reconciliation of Adjusted EBITDA:
(Loss) income before income taxes	(33,000,000.0)	13,300,000	(61,100,000)	27,600,000
Net income attributable to non-controlling interests	(27,300,000)	(26,600,000)	(75,000,000.0)	(78,100,000)
Depreciation and amortization	24,100,000	18,400,000	69,300,000	56,300,000
Interest expense, net	51,500,000	45,700,000	147,800,000	134,100,000
Equity-based compensation expense	3,000,000.0	2,700,000	9,900,000	7,600,000
Transaction, integration and practice acquisition costs	7,500,000	5,300,000	30,200,000	16,800,000
Impairment charges	33,500,000	0	33,500,000	0
Loss (gain) on disposals and deconsolidations, net	700,000	600,000	7,100,000	(7,000,000.0)
Litigation settlement and other litigation costs	1,100,000	2,800,000	4,900,000	2,800,000
Gain on escrow release	0	0	(800,000)	0
Loss on debt extinguishment	0	0	0	11,700,000
Tax receivable agreement expense	0	0	0	2,400,000
Impact of grant funds	5,400,000	0	(21,900,000)	0
Adjusted EBITDA excluding grant funds	66,500,000	62,200,000	143,900,000	174,200,000
Transaction and integration costs	5,400,000	3,400,000	15,800,000	11,600,000
Acquisition costs	2,100,000	1,900,000	14,400,000	5,200,000
Other litigation costs	1,100,000	2,800,000	3,700,000	2,800,000
Litigation settlement	0	0	1,200,000	0	$ 46,000,000.0
Operating Segments | Surgical Facility Services
Segment Reporting Information [Line Items]
Revenues	478,600,000	431,100,000	1,262,800,000	1,250,900,000
Adjusted EBITDA	82,500,000	77,100,000	229,700,000	223,900,000
Operating Segments | Ancillary Services
Segment Reporting Information [Line Items]
Revenues	16,700,000	20,000,000.0	46,900,000	60,300,000
Adjusted EBITDA	(600,000)	900,000	(3,900,000)	3,500,000
Operating Segments | Optical services revenues
Segment Reporting Information [Line Items]
Revenues	800,000	900,000	2,100,000	3,000,000.0
Adjusted EBITDA	400,000	400,000	1,000,000.0	1,300,000
All other
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (21,200,000)	$ (16,200,000)	$ (61,000,000.0)	$ (54,500,000)