Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) clinic	Mar. 31, 2021 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 5,166	$ 3,668
Goodwill deductible for tax purposes associated with acquisitions	4,442
Other current liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	9,238
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	24,955
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 34,193
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	$ 71,645
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	$ 5,166
Contingent earn-out obligations and liabilities assumed associated with acquisitions	245
Deferred purchase price obligations	$ 2,251
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	3