Acquisitions and divestitures - Additional Information (Detail) $ in Thousands		3 Months Ended		9 Months Ended
	May 01, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) clinic	Sep. 30, 2019 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses				$ 112,597	$ 77,348
Loss on changes in ownership interest, net		$ 0	$ 0	(16,252)	$ 0
Other current liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations		7,400		7,400
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations		18,914		18,914
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations		26,314		$ 26,314
Minimum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period				1 year
Maximum
Business Acquisition [Line Items]
Contingent earn-out obligations and liabilities assumed associated with acquisitions				$ 37,467
Maximum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period				5 years
RMS Lifeline
Business Acquisition [Line Items]
Loss on changes in ownership interest, net	$ (16,252)
Noncompete Agreements
Business Acquisition [Line Items]
Amortizable intangible assets acquired, weighted-average estimated useful lives				5 years
Dialysis and other businesses
Business Acquisition [Line Items]
Cash paid to acquire businesses				$ 112,597
Deferred purchase price obligations				6,917
Contingent earn-out obligations and liabilities assumed associated with acquisitions				21,021
Goodwill deductible for tax purposes associated with acquisitions		$ 91,157		$ 91,157
U.S. dialysis | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic				8
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic				36