Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) clinic	Mar. 31, 2019 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 34,107	$ 11,274
Other accrued liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	4,579
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	17,807
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 22,386
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	$ 31,723
Maximum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period	5 years
Noncompete Agreements
Business Acquisition [Line Items]
Amortizable intangible assets acquired, weighted-average estimated useful lives	4 years
Dialysis and other businesses
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 34,107
Deferred purchase price obligations	875
Contingent earn-out obligations and liabilities assumed associated with acquisitions	5,007
Goodwill deductible for tax purposes associated with acquisitions	$ 11,241
U.S. dialysis and related lab services | 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	22