Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) clinic	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses			$ 45,143	$ 112,597
Goodwill deductible for tax purposes associated with acquisitions	$ 49,501		49,501
Additional tax benefits recognized under the Coronavirus Aid, Relied, and Economic Security Act	0	$ 0	0	$ 9,980
Other current liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	7,420		7,420
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	15,337		15,337
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 22,757		$ 22,757
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			$ 35,941
Maximum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period			5 years
Dialysis and other businesses
Business Acquisition [Line Items]
Cash paid to acquire businesses			$ 45,143
Contingent earn-out obligations and liabilities assumed associated with acquisitions			3,181
Deferred purchase price obligations			$ 8,626
U.S. dialysis | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic			2
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic			10