Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) clinic	Sep. 30, 2018 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 77,348	$ 113,526
Deferred purchase price obligations	19,818
Contingent earn-out obligations and liabilities assumed associated with acquisitions	35,338
Other accrued liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	4,401
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	15,432
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 19,833
Minimum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period	1 year
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	$ 75,323
Deferred purchase price obligations	529
Goodwill deductible for tax purposes associated with acquisitions	$ 75,529
Noncompete Agreements
Business Acquisition [Line Items]
Amortizable intangible assets acquired, weighted-average estimated useful lives	6 years
U.S. dialysis and related lab services | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	7
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	9